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/mobile_dashboard_screen.dart

@@ -28,25 +28,10 @@ class _MobileDashboardScreenState extends ConsumerState<MobileDashboardScreen> {
   Widget build(BuildContext context) {
     final currentIndex = ref.watch(mobileDashboardIndexProvider);
 
-    // Determine which tab to show
-    Widget currentTab;
-    switch (currentIndex) {
-      case 0:
-        currentTab = MobileLiveTVTab(playlist: widget.playlist);
-        break;
-      case 1:
-        currentTab = MobileMoviesTab(playlist: widget.playlist);
-        break;
-      case 2:
-        currentTab = MobileSeriesTab(playlist: widget.playlist);
-        break;
-      case 3:
-        currentTab = const MobileSettingsTab();
-        break;
-      default:
-        currentTab = MobileLiveTVTab(playlist: widget.playlist);
-    }
-
+    // [P0-3 FIX] Use IndexedStack to preserve tab state and scroll position
+    // Instead of destroying/recreating tabs on each switch, keep all tabs alive in memory
+    // This enables instant tab switching and preserves user scroll position, search state, etc.
+    // The AutomaticKeepAliveClientMixin in each tab will keep them in the widget tree
     return Theme(
       data: MobileTheme.darkTheme,
       child: MobileScaffold(
@@ -54,7 +39,30 @@ class _MobileDashboardScreenState extends ConsumerState<MobileDashboardScreen> {
         onIndexChanged: (index) {
           ref.read(mobileDashboardIndexProvider.notifier).state = index;
         },
-        child: currentTab,
+        child: IndexedStack(
+          index: currentIndex,
+          children: [
+            // Tab 0: Live TV - stays alive to preserve channel list scroll position
+            MobileLiveTVTab(
+              key: const PageStorageKey('live_tv_tab'),
+              playlist: widget.playlist,
+            ),
+            // Tab 1: Movies - stays alive to preserve search and filter state
+            MobileMoviesTab(
+              key: const PageStorageKey('movies_tab'),
+              playlist: widget.playlist,
+            ),
+            // Tab 2: Series - stays alive to preserve series browsing state
+            MobileSeriesTab(
+              key: const PageStorageKey('series_tab'),
+              playlist: widget.playlist,
+            ),
+            // Tab 3: Settings - stays alive to preserve settings scroll position
+            const MobileSettingsTab(
+              key: PageStorageKey('settings_tab'),
+            ),
+          ],
+        ),
       ),
     );
   }

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();
   }