feat: add core UI components, login screen, and live TV tab

lib/core/widgets/components/ui_components.dart

@@ -218,10 +218,10 @@ class _ShimmerLoadingState extends State<ShimmerLoading>
             gradient: LinearGradient(
               begin: Alignment(_animation.value - 1, 0),
               end: Alignment(_animation.value + 1, 0),
-              colors: const [
-                AppColors.surfaceVariant,
+              colors: [
+                AppColors.surface.withOpacity(0.5),
                 AppColors.surface,
-                AppColors.surfaceVariant,
+                AppColors.surface.withOpacity(0.5),
               ],
             ),
           ),
@@ -280,7 +280,7 @@ class CategoryChip extends StatelessWidget {
     return Material(
       color: isSelected
           ? AppColors.primary.withOpacity(0.2)
-          : AppColors.surfaceVariant,
+          : AppColors.surface,
       borderRadius: BorderRadius.circular(AppTheme.radiusFull),
       child: InkWell(
         onTap: onTap,

lib/features/auth/screens/login_screen.dart

@@ -145,7 +145,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
                                 labelText: 'Username',
                                 prefixIcon: const Icon(Icons.person_outline),
                                 fillColor: AppColors.surface,
-                                hoverColor: AppColors.surfaceLight,
+                                hoverColor: AppColors.surface.withOpacity(0.8),
                               ),
                               validator: (value) {
                                 if (value == null || value.trim().isEmpty) {

lib/features/iptv/widgets/live_tv_tab.dart

@@ -153,7 +153,7 @@ class _LiveTVTabState extends ConsumerState<LiveTVTab>
                     : null,
                 isDense: true,
                 filled: true,
-                fillColor: AppColors.surfaceVariant,
+                fillColor: AppColors.surface.withOpacity(0.5),
                 border: OutlineInputBorder(
                   borderRadius: BorderRadius.circular(8),
                   borderSide: BorderSide.none,
@@ -238,7 +238,7 @@ class _LiveTVTabState extends ConsumerState<LiveTVTab>
                 begin: Alignment.topLeft,
                 end: Alignment.bottomRight,
                 colors: [
-                  AppColors.surfaceLight,
+                  AppColors.surface.withOpacity(0.8),
                   AppColors.surface,
                 ],
               ),
@@ -313,7 +313,7 @@ class _LiveTVTabState extends ConsumerState<LiveTVTab>
           Container(
             width: double.infinity,
             padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
-            color: AppColors.surfaceVariant.withOpacity(0.5),
+            color: AppColors.surface.withOpacity(0.5),
             child: Row(
               children: [
                 IconButton(