feat: Implement window size save scheduling to enhance window management

lib/app.dart

@@ -41,6 +41,7 @@ class _NotesAppState extends State<NotesApp>
   static const Duration _screenTransitionDuration = Duration(milliseconds: 280);
   static const Duration _biometricInactivityTimeout = Duration(minutes: 5);
   static const Duration _syncInterval = Duration(minutes: 5);
+  static const Duration _windowSizeSaveDelay = Duration(milliseconds: 350);
   static const String _themeSeedColorKey = 'theme_seed_color_v1';
 
   final LocalVaultService _vaultService = LocalVaultService.instance;
@@ -56,6 +57,7 @@ class _NotesAppState extends State<NotesApp>
   bool _biometricGateEnabled = false;
   int _biometricGateSession = 0;
   Timer? _biometricLockTimer;
+  Timer? _windowSizeSaveTimer;
   Timer? _syncTimer;
   bool _isHandlingWindowClose = false;
   _AppPhase _phase = _AppPhase.loading;
@@ -88,6 +90,7 @@ class _NotesAppState extends State<NotesApp>
       windowManager.setPreventClose(false);
     }
     _biometricLockTimer?.cancel();
+    _windowSizeSaveTimer?.cancel();
     _syncTimer?.cancel();
     _database?.close();
     super.dispose();
@@ -123,7 +126,8 @@ class _NotesAppState extends State<NotesApp>
   // Cached ThemeData to avoid recomputing on every build.
   ThemeData? _themeData;
 
-  ThemeData get _theme => _themeData ??= AppTheme.theme(seedColor: _themeSeedColor);
+  ThemeData get _theme =>
+      _themeData ??= AppTheme.theme(seedColor: _themeSeedColor);
 
   @override
   void didChangeAppLifecycleState(AppLifecycleState state) {
@@ -667,6 +671,22 @@ class _NotesAppState extends State<NotesApp>
     await WindowStateStore.instance.saveWindowSize(currentSize);
   }
 
+  void _scheduleWindowSizeSave() {
+    if (!isDesktop) {
+      return;
+    }
+
+    _windowSizeSaveTimer?.cancel();
+    _windowSizeSaveTimer = Timer(_windowSizeSaveDelay, () {
+      _windowSizeSaveTimer = null;
+      if (!mounted) {
+        return;
+      }
+
+      unawaited(_saveWindowSize());
+    });
+  }
+
   void _startPeriodicSync() {
     _syncTimer?.cancel();
     _syncTimer = Timer.periodic(_syncInterval, (_) {
@@ -888,12 +908,12 @@ class _NotesAppState extends State<NotesApp>
 
   @override
   void onWindowResize() {
-    _saveWindowSize();
+    _scheduleWindowSizeSave();
   }
 
   @override
   void onWindowResized() {
-    _saveWindowSize();
+    _scheduleWindowSizeSave();
   }
 
   @override
@@ -912,6 +932,10 @@ class _NotesAppState extends State<NotesApp>
       return;
     }
 
+    _windowSizeSaveTimer?.cancel();
+    _windowSizeSaveTimer = null;
+    unawaited(_saveWindowSize());
+
     if (!_needsBiometricLock) {
       unawaited(_allowWindowClose());
       return;