feat: Add theme customization options in settings screen and update app theme logic

lib/app.dart

@@ -19,6 +19,7 @@ import 'package:notas/widgets/app_title_bar.dart';
 import 'package:notas/widgets/sync_status_indicator.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 import 'package:window_manager/window_manager.dart';
 
 enum _AppSection {
@@ -50,6 +51,7 @@ 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 String _themeSeedColorKey = 'theme_seed_color_v1';
 
   final LocalVaultService _vaultService = LocalVaultService.instance;
   final GlobalKey<ScaffoldMessengerState> _scaffoldMessengerKey =
@@ -71,6 +73,7 @@ class _NotesAppState extends State<NotesApp>
   SyncStatus _syncStatus = SyncStatus.idle;
   String? _syncErrorMessage;
   int _homeRefreshToken = 0;
+  Color _themeSeedColor = Colors.amber;
 
   @override
   void initState() {
@@ -80,6 +83,7 @@ class _NotesAppState extends State<NotesApp>
       windowManager.addListener(this);
       windowManager.setPreventClose(true);
     }
+    _loadThemeSeedColor();
     _bootstrapVault();
   }
 
@@ -96,6 +100,33 @@ class _NotesAppState extends State<NotesApp>
     super.dispose();
   }
 
+  Future<void> _loadThemeSeedColor() async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    final int? storedColorValue = prefs.getInt(_themeSeedColorKey);
+    if (storedColorValue == null || !mounted) {
+      return;
+    }
+
+    setState(() {
+      _themeSeedColor = Color(storedColorValue);
+    });
+  }
+
+  Future<void> _setThemeSeedColor(Color color) async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    await prefs.setInt(_themeSeedColorKey, color.value);
+
+    if (!mounted) {
+      return;
+    }
+
+    setState(() {
+      _themeSeedColor = color;
+    });
+  }
+
+  ThemeData get _theme => AppTheme.theme(seedColor: _themeSeedColor);
+
   @override
   void didChangeAppLifecycleState(AppLifecycleState state) {
     if (_isUnlocking) {
@@ -669,7 +700,7 @@ class _NotesAppState extends State<NotesApp>
       navigatorKey: _navigatorKey,
       title: 'Mis Notas',
       debugShowCheckedModeBanner: false,
-      theme: AppTheme.theme,
+      theme: _theme,
       home: const Scaffold(
         body: SafeArea(
           child: Column(
@@ -700,7 +731,7 @@ class _NotesAppState extends State<NotesApp>
       title: 'Mis Notas',
       debugShowCheckedModeBanner: false,
       scaffoldMessengerKey: _scaffoldMessengerKey,
-      theme: AppTheme.theme,
+      theme: _theme,
       home: home,
     );
   }
@@ -722,6 +753,8 @@ class _NotesAppState extends State<NotesApp>
             onDeleteAllData: _resetLocalVaultData,
             onBackToHome: _openHome,
             onForceSync: () => _performSync(forceFull: true),
+            currentSeedColor: _themeSeedColor,
+            onThemeColorSelected: _setThemeSeedColor,
           );
 
     return MaterialApp(
@@ -729,7 +762,7 @@ class _NotesAppState extends State<NotesApp>
       title: 'Mis Notas',
       debugShowCheckedModeBanner: false,
       scaffoldMessengerKey: _scaffoldMessengerKey,
-      theme: AppTheme.theme,
+      theme: _theme,
       home: Shortcuts(
         shortcuts: <LogicalKeySet, Intent>{
           LogicalKeySet(LogicalKeyboardKey.f5): const PerformSyncIntent(),