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/BrentPriceResource.php

@@ -2,6 +2,7 @@
 
 namespace App\Filament\Resources;
 
+use App\Filament\NavigationGroup;
 use App\Filament\Resources\BrentPriceResource\Pages\ListBrentPrices;
 use App\Models\BrentPrice;
 use Filament\Resources\Resource;
@@ -12,9 +13,7 @@ class BrentPriceResource extends Resource
 {
     protected static ?string $model = BrentPrice::class;
 
-    protected static string|\BackedEnum|null $navigationIcon = 'heroicon-o-currency-dollar';
-
-    protected static string|\UnitEnum|null $navigationGroup = 'Data';
+    protected static string|\UnitEnum|null $navigationGroup = NavigationGroup::Data;
 
     protected static ?string $navigationLabel = 'Brent Prices';