Add user count column to residences admin page

- Add user_count field to ResidenceResponse DTO
- Update residence handler to preload Users and calculate count
- Count includes owner (1) plus all shared users
- Add Users column to admin residences list

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

admin/src/app/(dashboard)/residences/page.tsx

@@ -57,6 +57,10 @@ const columns: ColumnDef<Residence>[] = [
     accessorKey: 'owner_name',
     header: 'Owner',
   },
+  {
+    accessorKey: 'user_count',
+    header: 'Users',
+  },
   {
     accessorKey: 'city',
     header: 'Location',

admin/src/types/models.ts

@@ -109,6 +109,7 @@ export interface Residence {
   purchase_price?: number;
   is_primary: boolean;
   is_active: boolean;
+  user_count: number;
   created_at: string;
   updated_at: string;
 }