Phase 1 #24: Flutter 移动端框架（三合一 APP 骨架）

- pubspec.yaml: dio/provider/shared_preferences/flutter_map/geolocator
- main.dart: Provider 状态管理 + 登录守卫
- AuthService: Token 管理 + Dio HTTP + SharedPreferences 持久化
- LoginPage: Material Design 登录页
- HomePage: 三合一 BottomTab 导航（供水/巡检/营收）
- 预留依赖: flutter_local_notifications/image_picker/permission_handler

mobile/lib/services/auth_service.dart

@@ -0,0 +1,33 @@
+import 'package:flutter/foundation.dart';
+import 'package:dio/dio.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+class AuthService extends ChangeNotifier {
+  String _token = '';
+  bool get isLoggedIn => _token.isNotEmpty;
+
+  final Dio _dio = Dio(BaseOptions(baseUrl: 'http://10.0.2.2:8080/api/base'));
+
+  Future<bool> login(String username, String password) async {
+    try {
+      final res = await _dio.post('/auth/login', data: {'username': username, 'password': password});
+      if (res.data['code'] == 200) {
+        _token = res.data['data'];
+        final prefs = await SharedPreferences.getInstance();
+        await prefs.setString('token', _token);
+        notifyListeners();
+        return true;
+      }
+    } catch (e) {
+      debugPrint('Login failed: $e');
+    }
+    return false;
+  }
+
+  Future<void> logout() async {
+    _token = '';
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove('token');
+    notifyListeners();
+  }
+}