feat: 新增站内消息系统，支持通知与订单跳转

lib/core/notifications/keep_alive.dart

@@ -0,0 +1,25 @@
+import 'dart:io';
+
+import 'package:flutter/services.dart';
+
+/// Android 前台服务开关：让 App 在退到后台后仍保持进程存活，
+/// 从而继续轮询站内消息并弹系统通知。
+///
+/// 注意：这不是推送。用户手动「强行停止」/清理后台后服务会终止，
+/// 需要被杀进程后仍送达时必须接入厂商推送或极光/个推。
+class BackgroundKeepAlive {
+  BackgroundKeepAlive._();
+
+  static const _channel = MethodChannel('voltlink/keepalive');
+
+  static Future<void> setEnabled(bool enabled) async {
+    if (!Platform.isAndroid) return;
+    try {
+      await _channel.invokeMethod(enabled ? 'start' : 'stop');
+    } on PlatformException {
+      // 无通知权限或系统限制时静默失败，不影响主流程。
+    } on MissingPluginException {
+      // 非 Android 宿主或插件未注册。
+    }
+  }
+}

lib/core/notifications/local_notifications.dart

@@ -0,0 +1,98 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:flutter_local_notifications/flutter_local_notifications.dart';
+
+/// 本地系统通知。Android 专用（当前电工端只在 Android 分发）。
+///
+/// 只负责「展示通知」与「回传点击 payload」，消息从哪来由调用方决定。
+class LocalNotifications {
+  LocalNotifications._();
+
+  static final instance = LocalNotifications._();
+
+  static const channelId = 'voltlink_dispatch';
+  static const channelName = '派单与站内消息';
+  static const channelDesc = '收到新的派单或站内消息时提醒';
+
+  final _plugin = FlutterLocalNotificationsPlugin();
+  final _taps = StreamController<String>.broadcast();
+
+  /// 冷启动时由通知拉起的路由（初始化完成时读取一次）。
+  String? _launchRoute;
+
+  bool _ready = false;
+
+  /// 运行期点击通知的路由流。
+  Stream<String> get taps => _taps.stream;
+
+  /// 在 `runApp` 之前调用。
+  Future<void> init() async {
+    if (_ready || !Platform.isAndroid) return;
+    const settings = InitializationSettings(
+      android: AndroidInitializationSettings('@mipmap/ic_launcher'),
+    );
+    await _plugin.initialize(
+      settings: settings,
+      onDidReceiveNotificationResponse: _onTap,
+    );
+
+    final android = _plugin
+        .resolvePlatformSpecificImplementation<
+          AndroidFlutterLocalNotificationsPlugin
+        >();
+    // Android 13+ 需要用户授权，否则通知不会展示
+    await android?.requestNotificationsPermission();
+    await android?.createNotificationChannel(
+      const AndroidNotificationChannel(
+        channelId,
+        channelName,
+        description: channelDesc,
+        importance: Importance.high,
+      ),
+    );
+
+    final launch = await _plugin.getNotificationAppLaunchDetails();
+    if ((launch?.didNotificationLaunchApp ?? false)) {
+      final payload = launch?.notificationResponse?.payload;
+      if (payload != null && payload.isNotEmpty) _launchRoute = payload;
+    }
+    _ready = true;
+  }
+
+  /// 取出冷启动通知携带的路由（只返回一次）。
+  String? takeLaunchRoute() {
+    final route = _launchRoute;
+    _launchRoute = null;
+    return route;
+  }
+
+  Future<void> show({
+    required int id,
+    required String title,
+    required String body,
+    required String route,
+  }) async {
+    if (!_ready) return;
+    await _plugin.show(
+      id: id,
+      title: title,
+      body: body,
+      notificationDetails: const NotificationDetails(
+        android: AndroidNotificationDetails(
+          channelId,
+          channelName,
+          channelDescription: channelDesc,
+          importance: Importance.high,
+          priority: Priority.high,
+        ),
+      ),
+      payload: route,
+    );
+  }
+
+  void _onTap(NotificationResponse response) {
+    final payload = response.payload;
+    if (payload != null && payload.isNotEmpty) _taps.add(payload);
+  }
+}

lib/core/storage/token_storage.dart

@@ -13,6 +13,7 @@ class TokenStorage {
   static const _kUserInfo = 'userInfo';
   static const _kServerHost = 'serverHost';
   static const _kServerPort = 'serverPort';
+  static const _kNoticeAlertMaxId = 'noticeAlertMaxId';
 
   static Future<TokenStorage> open() async =>
       TokenStorage(await SharedPreferences.getInstance());
@@ -55,5 +56,11 @@ class TokenStorage {
     await _prefs.remove(_kUserInfo);
   }
 
+  /// 已弹过系统通知的最大消息 id，避免重启后重复提醒历史消息。
+  int get noticeAlertMaxId => _prefs.getInt(_kNoticeAlertMaxId) ?? -1;
+
+  Future<void> setNoticeAlertMaxId(int id) =>
+      _prefs.setInt(_kNoticeAlertMaxId, id);
+
   bool get hasSession => accessToken.isNotEmpty;
 }