refactor(ui): improve Apple TV aesthetics with premium gradients and glows

- Enhance category card gradient with teal accent (AppColors.primary)
- Add premium ambient glows to dashboard (teal + blue)
- Replace flat black background with subtle gradient for depth
- Increase glow intensity and size for better visual impact
- Apple TV inspired premium dark theme with accent lighting

Changes:
- live_tv_tab.dart: category gradient now uses AppColors.primary
- dashboard_screen.dart: add dual-glow background with premium styling

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

lib/features/iptv/widgets/live_tv_tab.dart

@@ -294,15 +294,15 @@ class _LiveTVTabState extends ConsumerState<LiveTVTab>
             padding: const EdgeInsets.all(0),
             child: Stack(
               children: [
-                // Background Gradient
+                // Background Gradient - Apple TV Style
                 Container(
                   decoration: BoxDecoration(
                     gradient: LinearGradient(
                       begin: Alignment.topLeft,
                       end: Alignment.bottomRight,
                       colors: [
-                        Colors.white.withOpacity(0.05),
-                        Colors.blue.withOpacity(0.05),
+                        AppColors.primary.withOpacity(0.15),
+                        AppColors.primary.withOpacity(0.05),
                       ],
                     ),
                   ),