refactor: 禁止 TenantId=0 并改为系统租户

src/Application/TakeoutSaaS.Application/Dictionary/Services/DictionaryAppService.cs

@@ -327,7 +327,7 @@ public sealed class DictionaryAppService(
         var tenantId = tenantProvider.GetCurrentTenantId();
         if (scope == DictionaryScope.System)
         {
-            EnsurePlatformTenant(tenantId);
+            EnsureSystemTenant(tenantId);
             return 0;
         }
 
@@ -362,9 +362,9 @@ public sealed class DictionaryAppService(
         }
     }
 
-    private void EnsurePlatformTenant(long tenantId)
+    private void EnsureSystemTenant(long tenantId)
     {
-        // 1. (空行后) 系统字典只能在平台租户（TenantId=0）上下文中操作
+        // 1. (空行后) 系统字典只能在系统租户（TenantId=0）上下文中操作
         if (tenantId != 0)
         {
             throw new BusinessException(ErrorCodes.Forbidden, "租户端不允许操作系统字典");

src/Domain/TakeoutSaaS.Domain/Tenants/Entities/Tenant.cs

@@ -5,7 +5,7 @@ using TakeoutSaaS.Shared.Abstractions.Entities;
 namespace TakeoutSaaS.Domain.Tenants.Entities;
 
 /// <summary>
-/// 平台租户信息，描述租户的生命周期与基础资料。
+/// 租户信息，描述租户的生命周期与基础资料。
 /// </summary>
 public sealed class Tenant : AuditableEntityBase
 {

src/Infrastructure/TakeoutSaaS.Infrastructure/App/Persistence/AppDataSeeder.cs

@@ -39,7 +39,7 @@ public sealed class AppDataSeeder(
         var appDbContext = scope.ServiceProvider.GetRequiredService<TakeoutAppDbContext>();
         var dictionaryDbContext = scope.ServiceProvider.GetRequiredService<DictionaryDbContext>();
 
-        await EnsurePlatformTenantAsync(appDbContext, cancellationToken);
+        await EnsureSystemTenantAsync(appDbContext, cancellationToken);
         var defaultTenantId = await EnsureDefaultTenantAsync(appDbContext, cancellationToken);
         await EnsureDictionarySeedsAsync(dictionaryDbContext, defaultTenantId, cancellationToken);
 
@@ -132,9 +132,9 @@ public sealed class AppDataSeeder(
     }
 
     /// <summary>
-    /// 确保平台租户存在。
+    /// 确保系统租户存在（TenantId=0，用于系统级数据归属）。
     /// </summary>
-    private async Task EnsurePlatformTenantAsync(TakeoutAppDbContext dbContext, CancellationToken cancellationToken)
+    private async Task EnsureSystemTenantAsync(TakeoutAppDbContext dbContext, CancellationToken cancellationToken)
     {
         var existingTenant = await dbContext.Tenants
             .IgnoreQueryFilters()
@@ -142,20 +142,47 @@ public sealed class AppDataSeeder(
 
         if (existingTenant != null)
         {
+            // 1. (空行后) 若历史数据仍为 PLATFORM，则自动修正为 SYSTEM
+            var updated = false;
+            if (!string.Equals(existingTenant.Code, "SYSTEM", StringComparison.Ordinal))
+            {
+                existingTenant.Code = "SYSTEM";
+                updated = true;
+            }
+
+            if (!string.Equals(existingTenant.Name, "System", StringComparison.Ordinal))
+            {
+                existingTenant.Name = "System";
+                updated = true;
+            }
+
+            if (existingTenant.Status != TenantStatus.Active)
+            {
+                existingTenant.Status = TenantStatus.Active;
+                updated = true;
+            }
+
+            if (updated)
+            {
+                dbContext.Tenants.Update(existingTenant);
+                await dbContext.SaveChangesAsync(cancellationToken);
+                logger.LogInformation("AppSeed 已更新系统租户 SYSTEM");
+            }
+
             return;
         }
 
         var tenant = new Tenant
         {
             Id = 0,
-            Code = "PLATFORM",
+            Code = "SYSTEM",
-            Name = "Platform",
+            Name = "System",
             Status = TenantStatus.Active
         };
 
         await dbContext.Tenants.AddAsync(tenant, cancellationToken);
         await dbContext.SaveChangesAsync(cancellationToken);
-        logger.LogInformation("AppSeed 已创建平台租户 PLATFORM");
+        logger.LogInformation("AppSeed 已创建系统租户 SYSTEM");
     }
 
     /// <summary>

src/Modules/TakeoutSaaS.Module.Tenancy/TenantResolutionMiddleware.cs

@@ -89,18 +89,25 @@ public sealed class TenantResolutionMiddleware(
     private static TenantContext ResolveTenant(HttpContext context, TenantResolutionOptions options)
     {
         var request = context.Request;
+        var isAuthenticated = context.User?.Identity?.IsAuthenticated == true;
 
         // 1. Token Claim（已认证请求必须以 Claim 为准，避免 Header 覆盖导致跨租户访问）
         var claim = context.User?.FindFirst("tenant_id");
-        if (claim != null && long.TryParse(claim.Value, out var claimTenant))
+        if (claim != null && long.TryParse(claim.Value, out var claimTenant) && claimTenant > 0)
         {
             return new TenantContext(claimTenant, null, "claim:tenant_id");
         }
+        // 1.1 (空行后) 已认证但缺少合法租户 Claim，则视为未解析（不允许 Header 覆盖）
+        if (isAuthenticated)
+        {
+            return TenantContext.Empty;
+        }
 
         // 2. Header 中的租户 ID
         if (!string.IsNullOrWhiteSpace(options.TenantIdHeaderName) &&
             request.Headers.TryGetValue(options.TenantIdHeaderName, out var tenantHeader) &&
-            long.TryParse(tenantHeader.FirstOrDefault(), out var headerTenantId))
+            long.TryParse(tenantHeader.FirstOrDefault(), out var headerTenantId) &&
+            headerTenantId > 0)
         {
             return new TenantContext(headerTenantId, null, $"header:{options.TenantIdHeaderName}");
         }
@@ -120,7 +127,7 @@ public sealed class TenantResolutionMiddleware(
         var host = request.Host.Host;
         if (!string.IsNullOrWhiteSpace(host))
         {
-            if (options.DomainTenantMap.TryGetValue(host, out var tenantFromHost))
+            if (options.DomainTenantMap.TryGetValue(host, out var tenantFromHost) && tenantFromHost > 0)
             {
                 return new TenantContext(tenantFromHost, null, $"host:{host}");
             }
@@ -143,7 +150,7 @@ public sealed class TenantResolutionMiddleware(
             return false;
         }
 
-        return options.CodeTenantMap.TryGetValue(code, out tenantId);
+        return options.CodeTenantMap.TryGetValue(code, out tenantId) && tenantId > 0;
     }
 
     private static string? ResolveCodeFromHost(string host, string? rootDomain)