feat: add UserResource with is_admin toggle and delete

User management resource with editable is_admin field, postcode support,
admin filter, and inline delete action. Includes list and edit pages.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Filament/Resources/UserResource.php

@@ -2,6 +2,7 @@
 
 namespace App\Filament\Resources;
 
+use App\Filament\NavigationGroup;
 use App\Filament\Resources\UserResource\Pages\EditUser;
 use App\Filament\Resources\UserResource\Pages\ListUsers;
 use App\Models\User;
@@ -20,7 +21,7 @@ class UserResource extends Resource
 {
     protected static ?string $model = User::class;
 
-    protected static string|\BackedEnum|null $navigationIcon = 'heroicon-o-users';
+    protected static string|\UnitEnum|null $navigationGroup = NavigationGroup::Users;
 
     protected static ?int $navigationSort = 1;