✨ feat: 完成账单管理模块后端功能开发及API优化

核心功能:
- 账单CRUD操作（创建、查询、详情、更新状态、删除）
- 支付记录管理（创建支付、审核支付）
- 批量操作支持（批量更新账单状态）
- 统计分析功能（账单统计、逾期账单查询）
- 导出功能（Excel/PDF/CSV）

API端点 (16个):
- GET /api/admin/v1/billings - 账单列表（分页、筛选、排序）
- POST /api/admin/v1/billings - 创建账单
- GET /api/admin/v1/billings/{id} - 账单详情
- DELETE /api/admin/v1/billings/{id} - 删除账单
- PUT /api/admin/v1/billings/{id}/status - 更新状态
- POST /api/admin/v1/billings/batch/status - 批量更新
- GET /api/admin/v1/billings/{id}/payments - 支付记录
- POST /api/admin/v1/billings/{id}/payments - 创建支付
- PUT /api/admin/v1/billings/payments/{paymentId}/verify - 审核支付
- GET /api/admin/v1/billings/statistics - 统计数据
- GET /api/admin/v1/billings/overdue - 逾期账单
- POST /api/admin/v1/billings/export - 导出账单

架构优化:
- 采用CQRS模式分离读写（MediatR + Dapper + EF Core）
- 完整的领域模型设计（TenantBillingStatement, TenantPayment等）
- FluentValidation请求验证
- 状态机管理账单和支付状态流转

API设计优化 (三项改进):
1. 导出API响应Content-Type改为application/octet-stream
2. 支付审核API添加Approved和Notes可选参数，支持通过/拒绝
3. 移除TenantBillings API中重复的TenantId参数

数据库变更:
- 新增账单相关表及关系
- 支持Snowflake ID主键
- 完整的审计字段支持

🤖 Generated with Claude Code

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/Infrastructure/TakeoutSaaS.Infrastructure/Migrations/20251217160046_UpdateTenantBillingSchema.cs

@@ -0,0 +1,237 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace TakeoutSaaS.Infrastructure.Migrations
+{
+    /// <inheritdoc />
+    public partial class UpdateTenantBillingSchema : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "RefundReason",
+                table: "tenant_payments",
+                type: "character varying(512)",
+                maxLength: 512,
+                nullable: true,
+                comment: "退款原因。");
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "RefundedAt",
+                table: "tenant_payments",
+                type: "timestamp with time zone",
+                nullable: true,
+                comment: "退款时间。");
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "VerifiedAt",
+                table: "tenant_payments",
+                type: "timestamp with time zone",
+                nullable: true,
+                comment: "审核时间。");
+
+            migrationBuilder.AddColumn<long>(
+                name: "VerifiedBy",
+                table: "tenant_payments",
+                type: "bigint",
+                nullable: true,
+                comment: "审核人 ID（管理员）。");
+
+            migrationBuilder.AlterColumn<decimal>(
+                name: "AmountDue",
+                table: "tenant_billing_statements",
+                type: "numeric(18,2)",
+                precision: 18,
+                scale: 2,
+                nullable: false,
+                comment: "应付金额（原始金额）。",
+                oldClrType: typeof(decimal),
+                oldType: "numeric(18,2)",
+                oldPrecision: 18,
+                oldScale: 2,
+                oldComment: "应付金额。");
+
+            migrationBuilder.AddColumn<int>(
+                name: "BillingType",
+                table: "tenant_billing_statements",
+                type: "integer",
+                nullable: false,
+                defaultValue: 0,
+                comment: "账单类型（订阅账单/配额包账单/手动账单/续费账单）。");
+
+            migrationBuilder.AddColumn<string>(
+                name: "Currency",
+                table: "tenant_billing_statements",
+                type: "character varying(8)",
+                maxLength: 8,
+                nullable: false,
+                defaultValue: "CNY",
+                comment: "货币类型（默认 CNY）。");
+
+            migrationBuilder.AddColumn<decimal>(
+                name: "DiscountAmount",
+                table: "tenant_billing_statements",
+                type: "numeric(18,2)",
+                precision: 18,
+                scale: 2,
+                nullable: false,
+                defaultValue: 0m,
+                comment: "折扣金额。");
+
+            migrationBuilder.AddColumn<string>(
+                name: "Notes",
+                table: "tenant_billing_statements",
+                type: "character varying(512)",
+                maxLength: 512,
+                nullable: true,
+                comment: "备注信息（如：人工备注、取消原因等）。");
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "OverdueNotifiedAt",
+                table: "tenant_billing_statements",
+                type: "timestamp with time zone",
+                nullable: true,
+                comment: "逾期通知时间。");
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "ReminderSentAt",
+                table: "tenant_billing_statements",
+                type: "timestamp with time zone",
+                nullable: true,
+                comment: "提醒发送时间（续费提醒、逾期提醒等）。");
+
+            migrationBuilder.AddColumn<long>(
+                name: "SubscriptionId",
+                table: "tenant_billing_statements",
+                type: "bigint",
+                nullable: true,
+                comment: "关联的订阅 ID（仅当 BillingType 为 Subscription 或 Renewal 时有值）。");
+
+            migrationBuilder.AddColumn<decimal>(
+                name: "TaxAmount",
+                table: "tenant_billing_statements",
+                type: "numeric(18,2)",
+                precision: 18,
+                scale: 2,
+                nullable: false,
+                defaultValue: 0m,
+                comment: "税费金额。");
+
+            migrationBuilder.CreateIndex(
+                name: "idx_payment_billing_paidat",
+                table: "tenant_payments",
+                columns: new[] { "BillingStatementId", "PaidAt" });
+
+            migrationBuilder.CreateIndex(
+                name: "idx_payment_transaction_no",
+                table: "tenant_payments",
+                column: "TransactionNo",
+                filter: "\"TransactionNo\" IS NOT NULL");
+
+            migrationBuilder.CreateIndex(
+                name: "idx_billing_created_at",
+                table: "tenant_billing_statements",
+                column: "CreatedAt");
+
+            migrationBuilder.CreateIndex(
+                name: "idx_billing_status_duedate",
+                table: "tenant_billing_statements",
+                columns: new[] { "Status", "DueDate" },
+                filter: "\"Status\" IN (0, 2)");
+
+            migrationBuilder.CreateIndex(
+                name: "idx_billing_tenant_status_duedate",
+                table: "tenant_billing_statements",
+                columns: new[] { "TenantId", "Status", "DueDate" });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "idx_payment_billing_paidat",
+                table: "tenant_payments");
+
+            migrationBuilder.DropIndex(
+                name: "idx_payment_transaction_no",
+                table: "tenant_payments");
+
+            migrationBuilder.DropIndex(
+                name: "idx_billing_created_at",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropIndex(
+                name: "idx_billing_status_duedate",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropIndex(
+                name: "idx_billing_tenant_status_duedate",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "RefundReason",
+                table: "tenant_payments");
+
+            migrationBuilder.DropColumn(
+                name: "RefundedAt",
+                table: "tenant_payments");
+
+            migrationBuilder.DropColumn(
+                name: "VerifiedAt",
+                table: "tenant_payments");
+
+            migrationBuilder.DropColumn(
+                name: "VerifiedBy",
+                table: "tenant_payments");
+
+            migrationBuilder.DropColumn(
+                name: "BillingType",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "Currency",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "DiscountAmount",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "Notes",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "OverdueNotifiedAt",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "ReminderSentAt",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "SubscriptionId",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.DropColumn(
+                name: "TaxAmount",
+                table: "tenant_billing_statements");
+
+            migrationBuilder.AlterColumn<decimal>(
+                name: "AmountDue",
+                table: "tenant_billing_statements",
+                type: "numeric(18,2)",
+                precision: 18,
+                scale: 2,
+                nullable: false,
+                comment: "应付金额。",
+                oldClrType: typeof(decimal),
+                oldType: "numeric(18,2)",
+                oldPrecision: 18,
+                oldScale: 2,
+                oldComment: "应付金额（原始金额）。");
+        }
+    }
+}

src/Infrastructure/TakeoutSaaS.Infrastructure/Migrations/TakeoutAppDbContextModelSnapshot.cs

@@ -6221,13 +6221,17 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                     b.Property<decimal>("AmountDue")
                         .HasPrecision(18, 2)
                         .HasColumnType("numeric(18,2)")
-                        .HasComment("应付金额。");
+                        .HasComment("应付金额（原始金额）。");
 
                     b.Property<decimal>("AmountPaid")
                         .HasPrecision(18, 2)
                         .HasColumnType("numeric(18,2)")
                         .HasComment("实付金额。");
 
+                    b.Property<int>("BillingType")
+                        .HasColumnType("integer")
+                        .HasComment("账单类型（订阅账单/配额包账单/手动账单/续费账单）。");
+
                     b.Property<DateTime>("CreatedAt")
                         .HasColumnType("timestamp with time zone")
                         .HasComment("创建时间（UTC）。");
@@ -6236,6 +6240,14 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                         .HasColumnType("bigint")
                         .HasComment("创建人用户标识，匿名或系统操作时为 null。");
 
+                    b.Property<string>("Currency")
+                        .IsRequired()
+                        .ValueGeneratedOnAdd()
+                        .HasMaxLength(8)
+                        .HasColumnType("character varying(8)")
+                        .HasDefaultValue("CNY")
+                        .HasComment("货币类型（默认 CNY）。");
+
                     b.Property<DateTime?>("DeletedAt")
                         .HasColumnType("timestamp with time zone")
                         .HasComment("软删除时间（UTC），未删除时为 null。");
@@ -6244,6 +6256,11 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                         .HasColumnType("bigint")
                         .HasComment("删除人用户标识（软删除），未删除时为 null。");
 
+                    b.Property<decimal>("DiscountAmount")
+                        .HasPrecision(18, 2)
+                        .HasColumnType("numeric(18,2)")
+                        .HasComment("折扣金额。");
+
                     b.Property<DateTime>("DueDate")
                         .HasColumnType("timestamp with time zone")
                         .HasComment("到期日。");
@@ -6252,6 +6269,15 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                         .HasColumnType("text")
                         .HasComment("账单明细 JSON，记录各项费用。");
 
+                    b.Property<string>("Notes")
+                        .HasMaxLength(512)
+                        .HasColumnType("character varying(512)")
+                        .HasComment("备注信息（如：人工备注、取消原因等）。");
+
+                    b.Property<DateTime?>("OverdueNotifiedAt")
+                        .HasColumnType("timestamp with time zone")
+                        .HasComment("逾期通知时间。");
+
                     b.Property<DateTime>("PeriodEnd")
                         .HasColumnType("timestamp with time zone")
                         .HasComment("账单周期结束时间。");
@@ -6260,6 +6286,10 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                         .HasColumnType("timestamp with time zone")
                         .HasComment("账单周期开始时间。");
 
+                    b.Property<DateTime?>("ReminderSentAt")
+                        .HasColumnType("timestamp with time zone")
+                        .HasComment("提醒发送时间（续费提醒、逾期提醒等）。");
+
                     b.Property<string>("StatementNo")
                         .IsRequired()
                         .HasMaxLength(64)
@@ -6270,6 +6300,15 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                         .HasColumnType("integer")
                         .HasComment("当前付款状态。");
 
+                    b.Property<long?>("SubscriptionId")
+                        .HasColumnType("bigint")
+                        .HasComment("关联的订阅 ID（仅当 BillingType 为 Subscription 或 Renewal 时有值）。");
+
+                    b.Property<decimal>("TaxAmount")
+                        .HasPrecision(18, 2)
+                        .HasColumnType("numeric(18,2)")
+                        .HasComment("税费金额。");
+
                     b.Property<long>("TenantId")
                         .HasColumnType("bigint")
                         .HasComment("所属租户 ID。");
@@ -6284,9 +6323,19 @@ namespace TakeoutSaaS.Infrastructure.Migrations
 
                     b.HasKey("Id");
 
+                    b.HasIndex("CreatedAt")
+                        .HasDatabaseName("idx_billing_created_at");
+
+                    b.HasIndex("Status", "DueDate")
+                        .HasDatabaseName("idx_billing_status_duedate")
+                        .HasFilter("\"Status\" IN (0, 2)");
+
                     b.HasIndex("TenantId", "StatementNo")
                         .IsUnique();
 
+                    b.HasIndex("TenantId", "Status", "DueDate")
+                        .HasDatabaseName("idx_billing_tenant_status_duedate");
+
                     b.ToTable("tenant_billing_statements", null, t =>
                         {
                             t.HasComment("租户账单，用于呈现周期性收费。");
@@ -6555,6 +6604,15 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                         .HasColumnType("character varying(512)")
                         .HasComment("支付凭证 URL。");
 
+                    b.Property<string>("RefundReason")
+                        .HasMaxLength(512)
+                        .HasColumnType("character varying(512)")
+                        .HasComment("退款原因。");
+
+                    b.Property<DateTime?>("RefundedAt")
+                        .HasColumnType("timestamp with time zone")
+                        .HasComment("退款时间。");
+
                     b.Property<int>("Status")
                         .HasColumnType("integer")
                         .HasComment("支付状态。");
@@ -6576,8 +6634,23 @@ namespace TakeoutSaaS.Infrastructure.Migrations
                         .HasColumnType("bigint")
                         .HasComment("最后更新人用户标识，匿名或系统操作时为 null。");
 
+                    b.Property<DateTime?>("VerifiedAt")
+                        .HasColumnType("timestamp with time zone")
+                        .HasComment("审核时间。");
+
+                    b.Property<long?>("VerifiedBy")
+                        .HasColumnType("bigint")
+                        .HasComment("审核人 ID（管理员）。");
+
                     b.HasKey("Id");
 
+                    b.HasIndex("TransactionNo")
+                        .HasDatabaseName("idx_payment_transaction_no")
+                        .HasFilter("\"TransactionNo\" IS NOT NULL");
+
+                    b.HasIndex("BillingStatementId", "PaidAt")
+                        .HasDatabaseName("idx_payment_billing_paidat");
+
                     b.HasIndex("TenantId", "BillingStatementId");
 
                     b.ToTable("tenant_payments", null, t =>