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/data/app_database.dart

@@ -7,39 +7,70 @@ import 'package:path_provider/path_provider.dart';
 
 part 'app_database.g.dart';
 
+@DataClassName('DbCategory')
+class Categories extends Table {
+  TextColumn get uuid => text().unique()();
+  TextColumn get encryptedName => text().named('encrypted_name')();
+  IntColumn get serverVersion => integer().named('server_version').withDefault(const Constant(0))();
+    BoolColumn get isDeleted => boolean().named('is_deleted').withDefault(const Constant(false))();
+  DateTimeColumn get updatedAt => dateTime().named('updated_at')();
+
+  @override
+  Set<Column> get primaryKey => {uuid};
+}
+
 @DataClassName('DbNote')
 class Notes extends Table {
   IntColumn get id => integer().autoIncrement()();
+  TextColumn get uuid => text().unique()();
   TextColumn get title => text()();
   TextColumn get body => text()();
-  DateTimeColumn get createdAt => dateTime()();
-  DateTimeColumn get updatedAt => dateTime()();
+  DateTimeColumn get createdAt => dateTime().named('created_at')();
+  DateTimeColumn get updatedAt => dateTime().named('updated_at')();
   IntColumn get sortIndex => integer().named('sort_index')();
+  IntColumn get serverVersion => integer().named('server_version').withDefault(const Constant(0))();
+    BoolColumn get isDeleted => boolean().named('is_deleted').withDefault(const Constant(false))();
+  TextColumn get categoryId => text().nullable().named('category_id')();
 }
 
-@DriftDatabase(tables: [Notes])
+@DriftDatabase(tables: [Notes, Categories])
 class AppDatabase extends _$AppDatabase {
-  AppDatabase({required String encryptionKey}) : super(_openConnection(encryptionKey));
-
   @override
   int get schemaVersion => 1;
+  AppDatabase({required String encryptionKey}) : super(_openConnection(encryptionKey));
 
+  // ========== Categories ==========
+  Future<List<DbCategory>> getAllCategories() {
+    return (select(categories)..where((c) => c.isDeleted.equals(false))).get();
+  }
+
+  Future<int> upsertCategory(CategoriesCompanion category) {
+    return into(categories).insertOnConflictUpdate(category);
+  }
+
+  Future<void> deleteCategory(String uuid) {
+    return (update(categories)..where((c) => c.uuid.equals(uuid)))
+        .write(CategoriesCompanion(isDeleted: Value(true)));
+  }
+
+  // ========== Notes ==========
   Future<List<DbNote>> getAllNotes() {
-    return (select(notes)..orderBy([
-      (note) => OrderingTerm(expression: note.sortIndex),
-    ])).get();
+    return (select(notes)
+          ..orderBy([(note) => OrderingTerm(expression: note.sortIndex)])
+          ..where((n) => n.isDeleted.equals(false)))
+        .get();
   }
 
   Future<int> insertNoteAtTop(NotesCompanion note) {
     return transaction(() async {
-      await customStatement('UPDATE notes SET sort_index = sort_index + 1');
+      await customStatement('UPDATE notes SET sort_index = sort_index + 1 WHERE is_deleted = 0');
       return into(notes).insert(note.copyWith(sortIndex: const Value<int>(0)));
     });
   }
 
   Future<void> replaceAllNotes(List<NotesCompanion> noteList) {
     return transaction(() async {
-      await delete(notes).go();
+      await (delete(notes)..where((n) => n.isDeleted.equals(false))).go();
 
       for (final NotesCompanion note in noteList) {
         await into(notes).insert(note);
@@ -51,17 +82,20 @@ class AppDatabase extends _$AppDatabase {
     return update(notes).replace(note);
   }
 
+  Future<void> deleteNote(int id, int removedIndex) async {
+    await (update(notes)..where((n) => n.id.equals(id))).write(NotesCompanion(isDeleted: Value(true)));
+
+    await customStatement(
+      'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ? AND is_deleted = 0',
+      [removedIndex],
+    );
+  }
+
   Future<void> deleteNoteAndShift({
     required int id,
     required int removedIndex,
   }) {
-    return transaction(() async {
-      await (delete(notes)..where((note) => note.id.equals(id))).go();
-      await customStatement(
-        'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ?',
-        [removedIndex],
-      );
-    });
+    return deleteNote(id, removedIndex);
   }
 
   Future<void> moveNote({
@@ -76,12 +110,12 @@ class AppDatabase extends _$AppDatabase {
     return transaction(() async {
       if (oldIndex < newIndex) {
         await customStatement(
-          'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ? AND sort_index <= ?',
+          'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ? AND sort_index <= ? AND is_deleted = 0',
           [oldIndex, newIndex],
         );
       } else {
         await customStatement(
-          'UPDATE notes SET sort_index = sort_index + 1 WHERE sort_index >= ? AND sort_index < ?',
+          'UPDATE notes SET sort_index = sort_index + 1 WHERE sort_index >= ? AND sort_index < ? AND is_deleted = 0',
           [newIndex, oldIndex],
         );
       }
@@ -92,6 +126,15 @@ class AppDatabase extends _$AppDatabase {
       );
     });
   }
+
+  // ========== Sync helpers ==========
+  Future<List<DbNote>> getUnsyncedNotes() {
+    return (select(notes)..where((n) => n.isDeleted.equals(true) | n.serverVersion.equals(0))).get();
+  }
+
+  Future<List<DbCategory>> getUnsyncedCategories() {
+    return (select(categories)..where((c) => c.isDeleted.equals(true) | c.serverVersion.equals(0))).get();
+  }
 }
 
 LazyDatabase _openConnection(String encryptionKey) {