feat(client/auth): 登录/注册页 Enter 键导航与提交

登录:邮箱框回车 → 跳到密码框;密码框回车 → 直接登录(校验条件同主按钮)。
注册:邮箱框回车 → 发送验证码并聚焦验证码框;验证码满 6 位回车 → 进入设密码步
并聚焦密码框;密码框(≥6 位)回车 → 直接注册。

经 TextField.onSubmitted + FocusNode.requestFocus 实现;桌面端回车即触发。

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

client/lib/widgets/auth_screen.dart

@@ -128,6 +128,33 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
     }
   }
 
+  // ── Enter 键导航 / 提交 ───────────────────────────────────────────
+  // 登录:邮箱回车 → 跳密码;密码回车 → 直接登录(校验条件同主按钮 enabled)。
+  void _submitLogin() {
+    if (!_loading && _emailValid && _pw.text.isNotEmpty) _doLogin();
+  }
+
+  // 注册:邮箱回车 → 发码并跳验证码;验证码(6位)回车 → 进设密码步并聚焦密码;
+  // 密码(≥6位)回车 → 直接注册。
+  void _onRegisterEmailSubmit() {
+    if (_loading || !_emailValid) return;
+    if (!_sent) _sendCode();
+    _codeFocus.requestFocus();
+  }
+
+  void _onRegisterCodeSubmit() {
+    if (!_sent || _code.text.length != 6) return;
+    setState(() => _step = 1);
+    // step 1 的密码框在本帧之后才挂载,延到下一帧再聚焦。
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (mounted) _pwFocus.requestFocus();
+    });
+  }
+
+  void _submitRegister() {
+    if (!_loading && _pw.text.length >= 6) _doRegister();
+  }
+
   void _setMode(_AuthMode m) => setState(() {
         _mode = m;
         _step = 0;
@@ -335,12 +362,14 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
       kBareInput.copyWith(contentPadding: const EdgeInsets.symmetric(vertical: 13));
 
   // 密码输入 + 显示/隐藏切换(眼睛按钮)。
-  Widget _pwInput(PangolinScheme c, String hint) => Row(children: [
+  Widget _pwInput(PangolinScheme c, String hint, {VoidCallback? onSubmit}) => Row(children: [
         Expanded(
           child: TextField(
             controller: _pw,
             focusNode: _pwFocus,
             obscureText: !_pwVisible,
+            textInputAction: TextInputAction.done,
+            onSubmitted: onSubmit == null ? null : (_) => onSubmit(),
             decoration: _bare.copyWith(hintText: hint),
             onChanged: (_) => setState(() {}),
           ),
@@ -370,9 +399,12 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
   Widget _login(PangolinScheme c, AppText t) {
     return Column(crossAxisAlignment: CrossAxisAlignment.stretch, children: [
       _field(c, icon: PangolinIcons.mail, label: t.emailLabel, focused: _emailFocus.hasFocus,
-          child: TextField(controller: _email, focusNode: _emailFocus, decoration: _bare.copyWith(hintText: t.emailPh), onChanged: (_) => setState(() {}))),
+          child: TextField(controller: _email, focusNode: _emailFocus,
+              textInputAction: TextInputAction.next,
+              onSubmitted: (_) => _pwFocus.requestFocus(),
+              decoration: _bare.copyWith(hintText: t.emailPh), onChanged: (_) => setState(() {}))),
       const SizedBox(height: 16),
-      _field(c, icon: PangolinIcons.lock, label: t.pwLabel, focused: _pwFocus.hasFocus, child: _pwInput(c, t.pwPh)),
+      _field(c, icon: PangolinIcons.lock, label: t.pwLabel, focused: _pwFocus.hasFocus, child: _pwInput(c, t.pwPh, onSubmit: _submitLogin)),
       Align(
         alignment: Alignment.centerRight,
         child: Padding(
@@ -391,7 +423,10 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
       return Column(crossAxisAlignment: CrossAxisAlignment.stretch, children: [
         _field(c, icon: PangolinIcons.mail, label: t.emailLabel, focused: _emailFocus.hasFocus,
             child: Row(children: [
-              Expanded(child: TextField(controller: _email, focusNode: _emailFocus, decoration: _bare.copyWith(hintText: t.emailPh), onChanged: (_) => setState(() {}))),
+              Expanded(child: TextField(controller: _email, focusNode: _emailFocus,
+                  textInputAction: TextInputAction.next,
+                  onSubmitted: (_) => _onRegisterEmailSubmit(),
+                  decoration: _bare.copyWith(hintText: t.emailPh), onChanged: (_) => setState(() {}))),
               GestureDetector(
                 onTap: (!_loading && _emailValid) ? _sendCode : null,
                 child: Text(_sent ? t.resend : t.sendCode,
@@ -410,6 +445,8 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
         const SizedBox(height: 16),
         _field(c, icon: PangolinIcons.shieldCheck, label: t.codeLabel, focused: _codeFocus.hasFocus,
             child: TextField(controller: _code, focusNode: _codeFocus, keyboardType: TextInputType.number, maxLength: 6,
+                textInputAction: TextInputAction.next,
+                onSubmitted: (_) => _onRegisterCodeSubmit(),
                 style: PangolinText.mono.copyWith(letterSpacing: 6, color: c.fg1),
                 decoration: _bare.copyWith(counterText: '', hintText: ''), onChanged: (_) => setState(() {}))),
         const SizedBox(height: 16),
@@ -434,7 +471,7 @@ class _AuthScreenState extends ConsumerState<AuthScreen>
         ]),
       ),
       const SizedBox(height: 16),
-      _field(c, icon: PangolinIcons.lock, label: t.pwLabel, focused: _pwFocus.hasFocus, child: _pwInput(c, t.setPwPh)),
+      _field(c, icon: PangolinIcons.lock, label: t.pwLabel, focused: _pwFocus.hasFocus, child: _pwInput(c, t.setPwPh, onSubmit: _submitRegister)),
       const SizedBox(height: 18),
       _primaryBtn(c, label: _loading ? '...' : t.doCreate,
           onPressed: (!_loading && _pw.text.length >= 6) ? _doRegister : null),