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/widgets/mobile_live_tv_tab.dart

@@ -37,9 +37,16 @@ class _MobileLiveTVTabState extends ConsumerState<MobileLiveTVTab>
   @override
   void initState() {
     super.initState();
+    // [P1-1 FIX] Debounce search input to prevent per-keystroke rebuilds
+    _searchTimer = null;
     _searchController.addListener(() {
-      setState(() {
-        _searchQuery = _searchController.text.toLowerCase();
+      _searchTimer?.cancel();
+      _searchTimer = Timer(const Duration(milliseconds: 500), () {
+        if (mounted) {
+          setState(() {
+            _searchQuery = _searchController.text.toLowerCase();
+          });
+        }
       });
     });
     // Trigger IP fetch for smart sorting
@@ -48,10 +55,13 @@ class _MobileLiveTVTabState extends ConsumerState<MobileLiveTVTab>
     });
   }
 
+  Timer? _searchTimer;
+
   @override
   void dispose() {
     _searchController.dispose();
     _searchFocusNode.dispose();
+    _searchTimer?.cancel();
     super.dispose();
   }