chore: integrate Hive for local storage management

- Added `hive_ce` and `hive_ce_flutter` dependencies for enhanced local storage capabilities.
- Refactored the main application to initialize Hive and migrate existing data.
- Updated storage service implementations to utilize Hive for managing application settings and task queues.
- Removed the deprecated `StorageService` class to streamline the codebase and improve maintainability.

lib/core/persistence/hive_bootstrap.dart

@@ -0,0 +1,46 @@
+import 'package:hive_ce_flutter/hive_flutter.dart';
+
+import 'hive_boxes.dart';
+
+/// Sets up Hive and exposes lazily opened boxes used across the app.
+class HiveBootstrap {
+  HiveBootstrap._();
+
+  static final HiveBootstrap instance = HiveBootstrap._();
+
+  HiveBoxes? _boxes;
+
+  /// Ensures Hive is initialized and all required boxes are open.
+  Future<HiveBoxes> ensureInitialized() async {
+    if (_boxes != null) {
+      return _boxes!;
+    }
+
+    await Hive.initFlutter('conduit_hive');
+
+    final preferences = await Hive.openBox<dynamic>(HiveBoxNames.preferences);
+    final caches = await Hive.openBox<dynamic>(HiveBoxNames.caches);
+    final attachmentQueue = await Hive.openBox<dynamic>(
+      HiveBoxNames.attachmentQueue,
+    );
+    final metadata = await Hive.openBox<dynamic>(HiveBoxNames.metadata);
+
+    _boxes = HiveBoxes(
+      preferences: preferences,
+      caches: caches,
+      attachmentQueue: attachmentQueue,
+      metadata: metadata,
+    );
+
+    return _boxes!;
+  }
+
+  /// Access the cached boxes after [ensureInitialized] has completed.
+  HiveBoxes get boxes {
+    final cached = _boxes;
+    if (cached == null) {
+      throw StateError('HiveBootstrap.ensureInitialized must run first.');
+    }
+    return cached;
+  }
+}