feat(client): 登录体验 — 记住邮箱 + 密码显隐 + 7天免登陆

1. 记住邮箱:登录页预填上次邮箱(TokenStore.saveLastEmail,登录/注册成功时存,
   退出登录不清除)。
2. 密码显隐:登录/注册密码框加眼睛按钮切换明文(PangolinIcons.eye/eyeOff)。
3. 7天免登陆:RootFlow 改为响应 authProvider——启动时有有效会话直接进主界面;
   AuthNotifier.refresh() 在服务端拒绝(refresh 过期/超 7 天)时 logout 回登录页,
   网络错误则保留会话。会话恢复期间显示极简启动屏。

flutter analyze 0 error;114 tests passed。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/test/golden/desktop_pages_golden_test.dart

@@ -30,6 +30,10 @@ class _NullTokenStore implements TokenStore {
   Future<void> markOnboarded() async {}
   @override
   Future<bool> isOnboarded() async => true;
+  @override
+  Future<void> saveLastEmail(String email) async {}
+  @override
+  Future<String?> loadLastEmail() async => null;
 }
 
 Future<void> _shoot(WidgetTester tester, NavView view, String name) async {

client/test/unit/connection_controller_test.dart

@@ -29,6 +29,10 @@ class _NullTokenStore implements TokenStore {
   Future<void> markOnboarded() async {}
   @override
   Future<bool> isOnboarded() async => true;
+  @override
+  Future<void> saveLastEmail(String email) async {}
+  @override
+  Future<String?> loadLastEmail() async => null;
 }
 
 // ── 辅助 ──────────────────────────────────────────────────────────

client/test/unit/nodes_provider_test.dart

@@ -23,6 +23,10 @@ class _NullTokenStore implements TokenStore {
   Future<void> markOnboarded() async {}
   @override
   Future<bool> isOnboarded() async => true;
+  @override
+  Future<void> saveLastEmail(String email) async {}
+  @override
+  Future<String?> loadLastEmail() async => null;
 }
 
 // 直接喂固定节点列表(不触发真实探针/HTTP)。

client/test/unit/quota_controller_test.dart

@@ -20,6 +20,10 @@ class _NullTokenStore implements TokenStore {
   Future<void> markOnboarded() async {}
   @override
   Future<bool> isOnboarded() async => true;
+  @override
+  Future<void> saveLastEmail(String email) async {}
+  @override
+  Future<String?> loadLastEmail() async => null;
 }
 
 ProviderContainer _container() => ProviderContainer(