Add contact settings and discovery features

- Implemented contact settings in localization files for Swedish, Ukrainian, and Chinese.
- Added new DiscoveryContact model to handle discovered contacts.
- Created DiscoveryScreen to display discovered contacts with filtering and sorting options.
- Integrated contact discovery storage to persist discovered contacts.
- Updated settings screen to include options for automatic contact addition.
- Enhanced app bar and list filter widgets for better user experience.
- Fixed variable naming inconsistencies in contact model.

lib/storage/contact_discovery_store.dart

@@ -0,0 +1,59 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+import '../models/discovery_contact.dart';
+import 'prefs_manager.dart';
+
+class ContactDiscoveryStore {
+  static const String _key = 'discovered_contacts';
+
+  Future<List<DiscoveryContact>> loadContacts() async {
+    final prefs = PrefsManager.instance;
+    final jsonStr = prefs.getString(_key);
+    if (jsonStr == null) return [];
+
+    try {
+      final jsonList = jsonDecode(jsonStr) as List<dynamic>;
+      return jsonList
+          .map((entry) => _fromJson(entry as Map<String, dynamic>))
+          .toList();
+    } catch (_) {
+      return [];
+    }
+  }
+
+  Future<void> saveContacts(List<DiscoveryContact> contacts) async {
+    final prefs = PrefsManager.instance;
+    final jsonList = contacts.map(_toJson).toList();
+    await prefs.setString(_key, jsonEncode(jsonList));
+  }
+
+  Map<String, dynamic> _toJson(DiscoveryContact contact) {
+    return {
+      'publicKey': base64Encode(contact.publicKey),
+      'name': contact.name,
+      'type': contact.type,
+      'pathLength': contact.pathLength,
+      'path': base64Encode(contact.path),
+      'latitude': contact.latitude,
+      'longitude': contact.longitude,
+      'lastSeen': contact.lastSeen.millisecondsSinceEpoch,
+    };
+  }
+
+  DiscoveryContact _fromJson(Map<String, dynamic> json) {
+    final lastSeenMs = json['lastSeen'] as int? ?? 0;
+    return DiscoveryContact(
+      publicKey: Uint8List.fromList(base64Decode(json['publicKey'] as String)),
+      name: json['name'] as String? ?? 'Unknown',
+      type: json['type'] as int? ?? 0,
+      pathLength: json['pathLength'] as int? ?? -1,
+      path: json['path'] != null
+          ? Uint8List.fromList(base64Decode(json['path'] as String))
+          : Uint8List(0),
+      latitude: (json['latitude'] as num?)?.toDouble(),
+      longitude: (json['longitude'] as num?)?.toDouble(),
+      lastSeen: DateTime.fromMillisecondsSinceEpoch(lastSeenMs),
+    );
+  }
+}