perf(critical): Implement P0 optimization fixes - TiviMate parity

CRITICAL FIXES:
- P0-1: Fix EPG N+1 query storm with batch loading
  * Implement XtreamServiceMobile with getBatchEPG() method
  * Batch load EPG data instead of per-channel requests
  * Reduce 50-200 concurrent requests to 1 request per category
  * Add EPG cache with 1-hour TTL to prevent redundant calls

- P0-2: Remove destructive cache clearing on startup
  * Implement TTL-based cache invalidation
  * Preserve cache between app launches (6h channels, 1h EPG, 30m search)
  * Add HiveService.invalidateExpiredCache() method
  * Expected: -80% startup time on cold launches

- P0-3: Preserve tab state with IndexedStack
  * Replace switch statement with IndexedStack
  * Keep all tabs alive in widget tree
  * Preserve scroll position, search state, filters across tab switches
  * Expected: instant tab switching (<100ms)

HIGH PRIORITY FIXES:
- P1-1: Debounce search input (500ms)
  * Prevent per-keystroke full rebuilds
  * Add search debounce timer

- P1-3: Fix double FocusNode disposal crash
  * Remove duplicate focus node disposal in native_player_screen.dart
  * Prevents StateError on player exit

Expected impact: -75-80% perceived latency, instant tab switching, no OOM on startup.

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

lib/features/iptv/screens/native_player_screen.dart

@@ -459,6 +459,8 @@ class _NativePlayerScreenState extends ConsumerState<NativePlayerScreen>
     _player.stop();
     _player.dispose();
     _xtreamService?.dispose();
+
+    // [P1-3 FIX] Dispose all focus nodes ONCE (was being disposed twice, causing crash)
     _playPauseFocusNode.dispose();
     _prevFocusNode.dispose();
     _nextFocusNode.dispose();
@@ -475,12 +477,6 @@ class _NativePlayerScreenState extends ConsumerState<NativePlayerScreen>
     ]);
     SystemChrome.setEnabledSystemUIMode(SystemUiMode.edgeToEdge);
 
-    // Dispose focus nodes
-    _playPauseFocusNode.dispose();
-    _prevFocusNode.dispose();
-    _nextFocusNode.dispose();
-    _backFocusNode.dispose();
-
     super.dispose();
   }