fix: 修复手机连不上服务器时启动页无限转圈（B-58）

- 启动页先读本地凭证：无凭证（首次打开）直接进登录页，不再先等 SDK 初始化
- SDK init/login 加 20s 超时；init 用共享 Future 防止超时后重复触发 initSDK
- 登录页对 IM 登录超时给出明确提示（确认手机连着公司内网 WiFi）
- 修复 flutter create 模板遗留的 widget_test（引用不存在的 MyApp），改为登录页渲染冒烟测试
- 版本号 1.0.1+2

mobile/test/widget_test.dart

@@ -1,30 +1,11 @@
-// This is a basic Flutter widget test.
-//
-// To perform an interaction with a widget in your test, use the WidgetTester
-// utility in the flutter_test package. For example, you can send tap and scroll
-// gestures. You can also use WidgetTester to find child widgets in the widget
-// tree, read text, and verify that the values of widget properties are correct.
-
+import 'package:changlian/screens/login_screen.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import 'package:changlian/main.dart';
-
 void main() {
-  testWidgets('Counter increments smoke test', (WidgetTester tester) async {
-    // Build our app and trigger a frame.
-    await tester.pumpWidget(const MyApp());
-
-    // Verify that our counter starts at 0.
-    expect(find.text('0'), findsOneWidget);
-    expect(find.text('1'), findsNothing);
-
-    // Tap the '+' icon and trigger a frame.
-    await tester.tap(find.byIcon(Icons.add));
-    await tester.pump();
-
-    // Verify that our counter has incremented.
-    expect(find.text('0'), findsNothing);
-    expect(find.text('1'), findsOneWidget);
+  testWidgets('登录页能正常渲染', (tester) async {
+    await tester.pumpWidget(const MaterialApp(home: LoginScreen()));
+    expect(find.text('畅联'), findsOneWidget);
+    expect(find.text('登录'), findsOneWidget);
   });
 }