feat: Introduce SearchableCategoryField component and integrate it into admin panels for enhanced category selection

flutter/lib/core/ui/app_shell.dart

@@ -12,13 +12,6 @@ const _profileHeaderDestination = _AppDestination(
   label: 'Profil',
 );
 
-const _adminHeaderDestination = _AppDestination(
-  path: '/admin',
-  title: 'Admin',
-  icon: Icons.admin_panel_settings_outlined,
-  label: 'Admin',
-);
-
 class AppShell extends ConsumerWidget {
   final String location;
   final ValueChanged<String> onNavigateToPath;
@@ -64,9 +57,7 @@ class AppShell extends ConsumerWidget {
     ),
   ];
 
-  List<_AppDestination> _destinations(bool isAdmin) => isAdmin
-      ? [..._baseDestinations, _adminHeaderDestination]
-      : _baseDestinations;
+  List<_AppDestination> _destinations() => _baseDestinations;
 
   int? _selectedIndex(List<_AppDestination> destinations) {
     final index = destinations.indexWhere(
@@ -77,14 +68,10 @@ class AppShell extends ConsumerWidget {
 
   _AppDestination _selectedHeaderDestination(
     List<_AppDestination> destinations,
-    bool isAdmin,
   ) {
     if (location.startsWith('/profile')) {
       return _profileHeaderDestination;
     }
-    if (location.startsWith('/admin') && isAdmin) {
-      return _adminHeaderDestination;
-    }
     final selectedIndex = _selectedIndex(destinations);
     if (selectedIndex != null) {
       return destinations[selectedIndex];
@@ -96,9 +83,9 @@ class AppShell extends ConsumerWidget {
   Widget build(BuildContext context, WidgetRef ref) {
     final locationUri = Uri.parse(location);
     final isAdmin = ref.watch(isAdminProvider);
-    final dests = _destinations(isAdmin);
+    final dests = _destinations();
     final selectedIndex = _selectedIndex(dests);
-    final selectedDestination = _selectedHeaderDestination(dests, isAdmin);
+    final selectedDestination = _selectedHeaderDestination(dests);
     final isWide = MediaQuery.of(context).size.width >= 900;
 
     void navigateTo(int index) {
@@ -210,6 +197,11 @@ class AppShell extends ConsumerWidget {
                     onNavigateToPath('/profile');
                   }
                   break;
+                case 'admin':
+                  if (location != '/admin' && context.mounted) {
+                    onNavigateToPath('/admin');
+                  }
+                  break;
                 case 'logout':
                   await ref.read(authStateProvider.notifier).logout();
                   if (context.mounted) {
@@ -227,6 +219,15 @@ class AppShell extends ConsumerWidget {
                   contentPadding: EdgeInsets.zero,
                 ),
               ),
+              if (isAdmin)
+                PopupMenuItem<String>(
+                  value: 'admin',
+                  child: ListTile(
+                    leading: Icon(Icons.admin_panel_settings_outlined),
+                    title: Text('Admin'),
+                    contentPadding: EdgeInsets.zero,
+                  ),
+                ),
               PopupMenuDivider(),
               PopupMenuItem<String>(
                 value: 'logout',