feat: 新增配额包/支付相关实体与迁移

App：新增 operation_logs/quota_packages/tenant_payments/tenant_quota_package_purchases 表

Identity：修正 Avatar 字段类型（varchar(256)->text），保持现有数据不变

src/Application/TakeoutSaaS.Application/App/Billings/BillingMapping.cs

@@ -0,0 +1,80 @@
+using TakeoutSaaS.Application.App.Billings.Dto;
+using TakeoutSaaS.Domain.Tenants.Entities;
+
+namespace TakeoutSaaS.Application.App.Billings;
+
+/// <summary>
+/// 账单 DTO 映射助手。
+/// </summary>
+internal static class BillingMapping
+{
+    /// <summary>
+    /// 将账单实体映射为账单 DTO。
+    /// </summary>
+    /// <param name="bill">账单实体。</param>
+    /// <param name="tenantName">租户名称。</param>
+    /// <returns>账单 DTO。</returns>
+    public static BillDto ToDto(this TenantBillingStatement bill, string? tenantName = null)
+        => new()
+        {
+            Id = bill.Id,
+            TenantId = bill.TenantId,
+            TenantName = tenantName,
+            StatementNo = bill.StatementNo,
+            PeriodStart = bill.PeriodStart,
+            PeriodEnd = bill.PeriodEnd,
+            AmountDue = bill.AmountDue,
+            AmountPaid = bill.AmountPaid,
+            Status = bill.Status,
+            DueDate = bill.DueDate,
+            CreatedAt = bill.CreatedAt
+        };
+
+    /// <summary>
+    /// 将账单实体与支付记录映射为账单详情 DTO。
+    /// </summary>
+    /// <param name="bill">账单实体。</param>
+    /// <param name="payments">支付记录列表。</param>
+    /// <param name="tenantName">租户名称。</param>
+    /// <returns>账单详情 DTO。</returns>
+    public static BillDetailDto ToDetailDto(
+        this TenantBillingStatement bill,
+        List<TenantPayment> payments,
+        string? tenantName = null)
+        => new()
+        {
+            Id = bill.Id,
+            TenantId = bill.TenantId,
+            TenantName = tenantName,
+            StatementNo = bill.StatementNo,
+            PeriodStart = bill.PeriodStart,
+            PeriodEnd = bill.PeriodEnd,
+            AmountDue = bill.AmountDue,
+            AmountPaid = bill.AmountPaid,
+            Status = bill.Status,
+            DueDate = bill.DueDate,
+            LineItemsJson = bill.LineItemsJson,
+            CreatedAt = bill.CreatedAt,
+            Payments = payments.Select(p => p.ToDto()).ToList()
+        };
+
+    /// <summary>
+    /// 将支付记录实体映射为支付 DTO。
+    /// </summary>
+    /// <param name="payment">支付记录实体。</param>
+    /// <returns>支付 DTO。</returns>
+    public static PaymentDto ToDto(this TenantPayment payment)
+        => new()
+        {
+            Id = payment.Id,
+            BillingStatementId = payment.BillingStatementId,
+            Amount = payment.Amount,
+            Method = payment.Method,
+            Status = payment.Status,
+            TransactionNo = payment.TransactionNo,
+            ProofUrl = payment.ProofUrl,
+            PaidAt = payment.PaidAt,
+            Notes = payment.Notes,
+            CreatedAt = payment.CreatedAt
+        };
+}