add support for badges and notifications, adjust nav pages

lib/services/data_service/data_service_notifications.dart

@@ -0,0 +1,62 @@
+part of 'data_service.dart';
+
+extension DataServiceNotifications on DataService {
+  Future<void> fetchNotifications() async {
+    _isNotificationsLoading = true;
+    try {
+      final json = await api.get('/notifications');
+      List<dynamic>? list;
+      if (json is List) {
+        list = json;
+      } else if (json is Map) {
+        for (final key in ['notifications', 'data', 'items']) {
+          final value = json[key];
+          if (value is List) {
+            list = value;
+            break;
+          }
+        }
+      }
+      final parsed = list
+          ?.whereType<Map<String, dynamic>>()
+          .map(UserNotification.fromJson)
+          .where((n) => !n.dismissed)
+          .toList();
+
+      if (parsed != null) {
+        parsed.sort((a, b) {
+          final aTs = a.createdAt?.millisecondsSinceEpoch ?? 0;
+          final bTs = b.createdAt?.millisecondsSinceEpoch ?? 0;
+          return bTs.compareTo(aTs);
+        });
+        _notifications = parsed;
+      } else {
+        _notifications = [];
+      }
+    } catch (e) {
+      debugPrint('Failed to fetch notifications: $e');
+      _notifications = [];
+    } finally {
+      _isNotificationsLoading = false;
+      _notifyAsync();
+    }
+  }
+
+  Future<void> dismissNotifications(List<int> notificationIds) async {
+    if (notificationIds.isEmpty) return;
+    try {
+      await api.put('/notifications/dismiss', {
+        "notification_ids": notificationIds,
+        "payload": {"dismissed": true},
+      });
+      _notifications = _notifications
+          .where((n) => !notificationIds.contains(n.id))
+          .toList();
+    } catch (e) {
+      debugPrint('Failed to dismiss notifications: $e');
+      rethrow;
+    } finally {
+      _notifyAsync();
+    }
+  }
+}