feat: Implement note encryption and synchronization features

- Added NoteEncryption class for encrypting and decrypting note content using AES-GCM.
- Updated NoteRepository to handle synchronization of notes and categories with the server, including encryption of note data before sending.
- Introduced SyncRequest and SyncResponse models for managing synchronization data.
- Enhanced LocalVaultService to store and retrieve the encryption key.
- Modified HomeScreen and SettingsScreen to trigger synchronization after note operations and manage API endpoint settings.
- Added SyncStatusIndicator to provide visual feedback on synchronization status in the app title bar.
- Created Category model to manage note categories with encryption support.
- Updated note model to include UUID, server version, deletion status, and category ID.
- Added necessary UI elements for displaying and managing the encryption key in SettingsScreen.
- Updated dependencies in pubspec.yaml for cryptography and HTTP handling.

lib/widgets/app_title_bar_stub.dart

@@ -1,7 +1,15 @@
 import 'package:flutter/material.dart';
+import 'package:notas/widgets/sync_status_indicator.dart';
 
 class AppTitleBar extends StatelessWidget {
-  const AppTitleBar({super.key});
+  const AppTitleBar({
+    this.syncStatus = SyncStatus.idle,
+    this.syncErrorMessage,
+    super.key,
+  });
+
+  final SyncStatus syncStatus;
+  final String? syncErrorMessage;
 
   @override
   Widget build(BuildContext context) {