feat: reorganize Filament into multi-panel structure and add is_admin cast

- Move Filament resources, pages, and widgets into Admin namespace subdirectories
- Remove default panel and login method calls from AdminPanelProvider
- Add is_admin boolean cast to User model

app/Providers/Filament/AdminPanelProvider.php

@@ -24,19 +24,17 @@ class AdminPanelProvider extends PanelProvider
     public function panel(Panel $panel): Panel
     {
         return $panel
-            ->default()
             ->id('admin')
             ->path('admin')
-            ->login()
             ->colors([
                 'primary' => Color::Amber,
             ])
-            ->discoverResources(in: app_path('Filament/Resources'), for: 'App\Filament\Resources')
-            ->discoverPages(in: app_path('Filament/Pages'), for: 'App\Filament\Pages')
+            ->discoverResources(in: app_path('Filament/Admin/Resources'), for: 'App\Filament\Admin\Resources')
+            ->discoverPages(in: app_path('Filament/Admin/Pages'), for: 'App\Filament\Admin\Pages')
             ->pages([
                 Dashboard::class,
             ])
-            ->discoverWidgets(in: app_path('Filament/Widgets'), for: 'App\Filament\Widgets')
+            ->discoverWidgets(in: app_path('Filament/Admin/Widgets'), for: 'App\Filament\Admin\Widgets')
             ->widgets([
                 AccountWidget::class,
                 FilamentInfoWidget::class,