fix(backend): update middleware ordering and interceptors for RLS

Update TenantValidationMiddleware, Program.cs startup sequence,
SaveChangesTenantInterceptor, and TenantProvider to ensure proper
middleware ordering and tenant context initialization before database access.

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/WorkClub.Infrastructure/Services/TenantProvider.cs

@@ -1,7 +1,5 @@
 using System.Security.Claims;
 using System.Text.Json;
-using Finbuckle.MultiTenant;
-using Finbuckle.MultiTenant.Abstractions;
 using Microsoft.AspNetCore.Http;
 using WorkClub.Application.Interfaces;
 
@@ -9,26 +7,22 @@ namespace WorkClub.Infrastructure.Services;
 
 public class TenantProvider : ITenantProvider
 {
-    private readonly IMultiTenantContextAccessor _multiTenantContextAccessor;
     private readonly IHttpContextAccessor _httpContextAccessor;
 
-    public TenantProvider(
-        IMultiTenantContextAccessor multiTenantContextAccessor,
-        IHttpContextAccessor httpContextAccessor)
+    public TenantProvider(IHttpContextAccessor httpContextAccessor)
     {
-        _multiTenantContextAccessor = multiTenantContextAccessor;
         _httpContextAccessor = httpContextAccessor;
     }
 
     public string GetTenantId()
     {
-        var tenantInfo = _multiTenantContextAccessor.MultiTenantContext?.TenantInfo;
-        if (tenantInfo == null || string.IsNullOrEmpty(tenantInfo.Identifier))
+        var tenantId = _httpContextAccessor.HttpContext?.Items["TenantId"] as string;
+        if (string.IsNullOrEmpty(tenantId))
         {
             throw new InvalidOperationException("Tenant context is not available");
         }
 
-        return tenantInfo.Identifier;
+        return tenantId;
     }
 
     public string GetUserRole()