refactor(theme): update color references to use AppColors for consistency across components

lib/features/admin/screens/admin_panel.dart

@@ -26,14 +26,13 @@ class AdminPanel extends StatelessWidget {
       extendBodyBehindAppBar: true,
       body: Container(
         decoration: const BoxDecoration(
-          gradient: RadialGradient(
-            center: Alignment.center,
-            radius: 1.5,
+          gradient: LinearGradient(
+            begin: Alignment.topCenter,
+            end: Alignment.bottomCenter,
             colors: [
-              Color(0xFF2C2C2E), // Dark Grey (Apple TV Surface)
-              Color(0xFF000000), // Pure Black
+              AppColors.surfaceVariant,
+              AppColors.background,
             ],
-            stops: [0.0, 1.0],
           ),
         ),
         child: const AdminContent(),

lib/features/auth/screens/login_screen.dart

@@ -54,15 +54,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
           // 1. Cinematic Background (Abstract Gradient)
           Container(
             decoration: const BoxDecoration(
-              gradient: LinearGradient(
-                begin: Alignment.topLeft,
-                end: Alignment.bottomRight,
-                colors: [
-                  Color(0xFF0D0D0D), // Almost Black
-                  Color(0xFF1A1A1A), // Dark Grey
-                  Color(0xFF0F0F0F), // Deep Dark
-                ],
-              ),
+              gradient: AppColors.backgroundGradient,
             ),
           ),
 
@@ -121,7 +113,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
                         gradient: const LinearGradient(
                           begin: Alignment.topLeft,
                           end: Alignment.bottomRight,
-                          colors: [Color(0xFF2C2C2E), Color(0xFF000000)],
+                          colors: [AppColors.surfaceVariant, AppColors.background],
                         ),
                         borderRadius: BorderRadius.circular(32),
                         boxShadow: [
@@ -134,7 +126,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
                       ),
                       child: const Icon(
                         Icons.play_arrow_rounded,
-                        color: Colors.white,
+                        color: AppColors.textPrimary,
                         size: 64,
                       ),
                     ),

lib/features/iptv/screens/dashboard_screen.dart

@@ -45,14 +45,7 @@ class _DashboardScreenState extends ConsumerState<DashboardScreen> {
           Positioned.fill(
             child: Container(
               decoration: const BoxDecoration(
-                gradient: LinearGradient(
-                  begin: Alignment.topLeft,
-                  end: Alignment.bottomRight,
-                  colors: [
-                    Color(0xFF0F1014), // Deep Space Blue-Grey
-                    Color(0xFF181920), // Darker shade
-                  ],
-                ),
+                gradient: AppColors.backgroundGradient,
               ),
             ),
           ),

lib/features/iptv/screens/playlist_selection_screen.dart

@@ -29,7 +29,7 @@ class PlaylistSelectionScreen extends ConsumerWidget {
           'Select Playlist',
           style: GoogleFonts.roboto(
             fontWeight: FontWeight.w600,
-            color: Colors.white,
+            color: AppColors.textPrimary,
           ),
         ),
         backgroundColor: Colors.transparent,
@@ -38,12 +38,12 @@ class PlaylistSelectionScreen extends ConsumerWidget {
           if (currentUser?.isAdmin ?? false)
             IconButton(
               icon:
-                  const Icon(Icons.admin_panel_settings, color: Colors.white70),
+                  const Icon(Icons.admin_panel_settings, color: AppColors.textSecondary),
               onPressed: () => context.go('/admin'),
               tooltip: 'Admin Panel',
             ),
           IconButton(
-            icon: const Icon(Icons.logout, color: Colors.white70),
+            icon: const Icon(Icons.logout, color: AppColors.textSecondary),
             onPressed: () async {
               await ref.read(authProvider.notifier).logout();
               if (context.mounted) {
@@ -56,14 +56,7 @@ class PlaylistSelectionScreen extends ConsumerWidget {
       ),
       body: Container(
         decoration: const BoxDecoration(
-          gradient: LinearGradient(
-            begin: Alignment.topLeft,
-            end: Alignment.bottomRight,
-            colors: [
-              Color(0xFF0F1014), // Deep Space Dark
-              Color(0xFF181920), // Soft Eerie Black
-            ],
-          ),
+          gradient: AppColors.backgroundGradient,
         ),
         child: playlistsAsync.when(
           loading: () => const Center(
@@ -80,7 +73,7 @@ class PlaylistSelectionScreen extends ConsumerWidget {
                   'Error loading playlists',
                   style: GoogleFonts.outfit(
                     fontSize: 18,
-                    color: Colors.white70,
+                    color: AppColors.textSecondary,
                   ),
                 ),
                 const SizedBox(height: 8),
@@ -88,7 +81,7 @@ class PlaylistSelectionScreen extends ConsumerWidget {
                   onPressed: () => ref.refresh(playlistsProvider),
                   style: ElevatedButton.styleFrom(
                     backgroundColor: AppColors.primary,
-                    foregroundColor: Colors.white,
+                    foregroundColor: AppColors.textPrimary,
                   ),
                   child: Text('Retry', style: GoogleFonts.inter()),
                 ),