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/lib/widgets/auth_screen.dart

@@ -32,6 +32,7 @@ class _AuthScreenState extends ConsumerState<AuthScreen> {
   int _step = 0;
   bool _sent = false;
   bool _loading = false;
+  bool _pwVisible = false;
   String? _errorZh;
 
   final _email = TextEditingController();
@@ -42,6 +43,17 @@ class _AuthScreenState extends ConsumerState<AuthScreen> {
 
   bool get _emailValid => RegExp(r'\S+@\S+\.\S+').hasMatch(_email.text);
 
+  @override
+  void initState() {
+    super.initState();
+    // 预填上次登录邮箱。
+    ref.read(tokenStoreProvider).loadLastEmail().then((email) {
+      if (email != null && email.isNotEmpty && mounted) {
+        setState(() => _email.text = email);
+      }
+    });
+  }
+
   @override
   void dispose() {
     _email.dispose();
@@ -71,6 +83,7 @@ class _AuthScreenState extends ConsumerState<AuthScreen> {
         code: _code.text.trim(),
         password: _pw.text,
       );
+      await ref.read(tokenStoreProvider).saveLastEmail(_email.text.trim());
       await ref.read(authProvider.notifier).saveTokens(tokens);
       if (mounted) widget.onDone();
     } on AuthApiException catch (e) {
@@ -85,6 +98,7 @@ class _AuthScreenState extends ConsumerState<AuthScreen> {
         email: _email.text.trim(),
         password: _pw.text,
       );
+      await ref.read(tokenStoreProvider).saveLastEmail(_email.text.trim());
       await ref.read(authProvider.notifier).saveTokens(tokens);
       if (mounted) widget.onDone();
     } on AuthApiException catch (e) {
@@ -182,13 +196,31 @@ class _AuthScreenState extends ConsumerState<AuthScreen> {
   InputDecoration get _bare =>
       const InputDecoration(border: InputBorder.none, isCollapsed: true, contentPadding: EdgeInsets.symmetric(vertical: 12));
 
+  // 密码输入 + 显示/隐藏切换(眼睛按钮)。
+  Widget _pwInput(PangolinScheme c, String hint) => Row(children: [
+        Expanded(
+          child: TextField(
+            controller: _pw,
+            obscureText: !_pwVisible,
+            decoration: _bare.copyWith(hintText: hint),
+            onChanged: (_) => setState(() {}),
+          ),
+        ),
+        GestureDetector(
+          onTap: () => setState(() => _pwVisible = !_pwVisible),
+          child: Padding(
+            padding: const EdgeInsets.only(left: 6),
+            child: Icon(_pwVisible ? PangolinIcons.eyeOff : PangolinIcons.eye, size: 18, color: c.fg3),
+          ),
+        ),
+      ]);
+
   Widget _login(PangolinScheme c, AppText t) {
     return Column(children: [
       _field(c, icon: PangolinIcons.mail, label: t.emailLabel,
           child: TextField(controller: _email, decoration: _bare.copyWith(hintText: t.emailPh), onChanged: (_) => setState(() {}))),
       const SizedBox(height: 16),
-      _field(c, icon: PangolinIcons.lock, label: t.pwLabel,
-          child: TextField(controller: _pw, obscureText: true, decoration: _bare.copyWith(hintText: t.pwPh), onChanged: (_) => setState(() {}))),
+      _field(c, icon: PangolinIcons.lock, label: t.pwLabel, child: _pwInput(c, t.pwPh)),
       Align(
         alignment: Alignment.centerRight,
         child: Padding(
@@ -239,8 +271,7 @@ class _AuthScreenState extends ConsumerState<AuthScreen> {
     return Column(children: [
       Row(children: [Icon(PangolinIcons.checkCircle, size: 15, color: c.success), const SizedBox(width: 7), Text(_email.text, style: PangolinText.sm.copyWith(color: c.fg2))]),
       const SizedBox(height: 16),
-      _field(c, icon: PangolinIcons.lock, label: t.pwLabel,
-          child: TextField(controller: _pw, obscureText: true, decoration: _bare.copyWith(hintText: t.setPwPh), onChanged: (_) => setState(() {}))),
+      _field(c, icon: PangolinIcons.lock, label: t.pwLabel, child: _pwInput(c, t.setPwPh)),
       const SizedBox(height: 18),
       PangolinButton(
         label: _loading ? '...' : t.doCreate,

client/lib/widgets/pangolin_icons.dart

@@ -18,6 +18,8 @@ class PangolinIcons {
 
   // ── 导航 / 操作 ──
   static const settings     = LucideIcons.settings;
+  static const eye          = LucideIcons.eye;
+  static const eyeOff       = LucideIcons.eyeOff;
   static const user         = LucideIcons.user;
   static const search       = LucideIcons.search;
   static const check        = LucideIcons.check;