fix: restore EPG display in live TV player and channel cards

- Fix EPG not showing in NativePlayerScreen by reusing the shared
  mobileXtreamServiceProvider (cache already populated by channel cards)
  instead of creating a fresh service instance per player session
- Add periodic EPG refresh timer (every 5 min) matching LitePlayerScreen
- Fix empty-title fallback in _buildEPGBox
- Force dark theme, invert default live TV player (NativePlayer default),
  remove next-program display from OSD
- Fix back button exit dialog firing from wrong tab (add tab index guards)
- Halve card grid count for Movies/Series (6 categories, 8 items)
- Revamp Movies/Series search bars to match Live TV aesthetic
- Fix first channel row clipping when entering a category (scroll-to-top)
- Fix playlist edit dialog TV remote navigation
- Fix empty playlist screen button readability
- Remove theme switcher from settings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/core/providers/theme_provider.dart

@@ -41,26 +41,8 @@ class ThemeNotifier extends StateNotifier<ThemeState> {
     _loadTheme();
   }
 
-  /// Load saved theme preference from SharedPreferences
-  Future<void> _loadTheme() async {
-    try {
-      final prefs = await SharedPreferences.getInstance();
-      final savedMode = prefs.getString(_ThemeKeys.themeMode);
-      
-      if (savedMode != null) {
-        final appMode = AppThemeMode.values.firstWhere(
-          (e) => e.name == savedMode,
-          orElse: () => AppThemeMode.dark,
-        );
-        state = state.copyWith(
-          appThemeMode: appMode,
-          themeMode: _mapToThemeMode(appMode),
-        );
-      }
-    } catch (e) {
-      debugPrint('Error loading theme: $e');
-    }
-  }
+  /// Theme is always forced to dark — no loading from preferences
+  Future<void> _loadTheme() async {}
 
   /// Set theme mode and persist to SharedPreferences
   Future<void> setThemeMode(AppThemeMode mode) async {