fix(infra): add explicit transaction management to TenantDbConnectionInterceptor for RLS

PostgreSQL SET LOCAL only persists within a transaction scope. Added explicit transaction creation if none exists, ensuring tenant context is properly set before queries execute. Fixes tenant isolation for multi-tenant RLS filtering.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

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

backend/WorkClub.Infrastructure/Data/Interceptors/TenantDbConnectionInterceptor.cs

@@ -1,3 +1,4 @@
+using System.Data;
 using System.Data.Common;
 using Microsoft.AspNetCore.Http;
 using Microsoft.EntityFrameworkCore.Diagnostics;
@@ -63,14 +64,40 @@ public class TenantDbConnectionInterceptor : DbCommandInterceptor
         
         if (!string.IsNullOrWhiteSpace(tenantId) && command.Connection is NpgsqlConnection conn)
         {
-            // Prepend SET LOCAL to set tenant context
+            try
-            // Note: EF Core creates implicit transactions for queries, so SET LOCAL will work
+            {
-            command.CommandText = $"SET LOCAL app.current_tenant_id = '{tenantId}'; " + command.CommandText;
+                // If no transaction exists AND connection is open, start one
-            _logger.LogInformation("SetTenantContext: Prepended SET LOCAL for tenant {TenantId}", tenantId);
+                // SET LOCAL only persists within a transaction, so we need explicit transaction scope
+                if (command.Transaction == null && conn.State == ConnectionState.Open)
+                {
+                    command.Transaction = (NpgsqlTransaction)conn.BeginTransaction();
+                    _logger.LogInformation("SetTenantContext: Started transaction for tenant context");
+                }
+                
+                // Execute SET LOCAL as a separate command on the same connection
+                // This ensures the session variable is properly set before the main query executes
+                using var setLocalCmd = conn.CreateCommand();
+                setLocalCmd.CommandText = $"SET LOCAL app.current_tenant_id = '{tenantId}'";
+                
+                // Use the same transaction if one exists (which it should now)
+                if (command.Transaction is NpgsqlTransaction transaction)
+                {
+                    setLocalCmd.Transaction = transaction;
+                }
+                
+                // Execute synchronously (safe in interceptor context)
+                setLocalCmd.ExecuteNonQuery();
+                _logger.LogInformation("SetTenantContext: Executed SET LOCAL for tenant {TenantId}", tenantId);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "SetTenantContext: Failed to execute SET LOCAL for tenant {TenantId}", tenantId);
+                throw;
+            }
         }
         else
         {
-            _logger.LogWarning("ReaderExecuting: No tenant context available (tenantId={TenantId})", tenantId ?? "null");
+            _logger.LogWarning("SetTenantContext: No tenant context available (tenantId={TenantId})", tenantId ?? "null");
         }
     }
 }