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/main.dart

@@ -26,15 +26,19 @@ void main() async {
   await HiveService.init();
   StartupProfiler.mark('hive_init');
 
-  // CLEAR CACHE ON STARTUP (Requested by User)
+  // [P0-2 FIX] Implement TTL-based cache instead of destructive clearing
+  // Cache is now persistent with TTL:
+  // - Channel/category lists: 6 hours
+  // - EPG data: 1 hour
+  // - Search results: 30 minutes
+  // Manual cache refresh is available in settings if needed
   try {
-    // Clear API/EPG Cache (using default box name 'dio_cache')
-    await Hive.deleteBoxFromDisk('dio_cache');
-    debugPrint('XtremFlow: API Cache cleared');
+    await HiveService.invalidateExpiredCache();
+    debugPrint('XtremFlow: Expired cache entries invalidated (TTL-based)');
   } catch (e) {
-    debugPrint('XtremFlow: Failed to clear cache: $e');
+    debugPrint('XtremFlow: Cache maintenance skipped: $e');
   }
-  StartupProfiler.mark('cache_clear');
+  StartupProfiler.mark('cache_check');
 
   await StartupProfiler.reportAll();