fix: 修正学习流程中的证据、复习与进度问题

- 独立尝试按课程要求校验内容，不再任意输入即算独立成功
- 复习节点改为学后第 1/3/7/14 天，之后每 30 天抽查；复习轮换情境
- 掌握状态按作答记录推导：需认识、可回忆、跨情境使用及最近两次无帮助
- 课程证据按实际用到的目标记录；跟读与课程对话只算辅助练习
- 复习成功不再降低已有状态
- 学完课程后进入下一节未完成课程；全部学完后引导巩固与阶段评估
- 新增 3 题基础定位，按结果设置起始课程
- 新增按课程开放的对话场景，首页推荐最少练习的场景
- 切换课程时清空上一课的步骤进度
- AI 返回 JSON 格式并按 JSON 回放历史；拼写校验忽略大小写与连字符；移除学习目标选择

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kouyu_english/lib/features/onboarding/onboarding_pages.dart

@@ -3,7 +3,11 @@ import 'package:flutter/material.dart';
 import '../../core/app_state.dart';
 import '../../core/app_theme.dart';
 import '../../core/models.dart';
+import '../../core/review_feedback.dart';
+import '../../core/seed_courses.dart';
+import '../../core/voice_service.dart';
 import '../../widgets/app_widgets.dart';
+import '../../widgets/voice_answer.dart';
 
 class WelcomePage extends StatefulWidget {
   const WelcomePage({super.key, required this.state, required this.onContinue});
@@ -16,13 +20,11 @@ class WelcomePage extends StatefulWidget {
 }
 
 class _WelcomePageState extends State<WelcomePage> {
-  late LearningGoal selectedGoal;
   late int selectedMinutes;
 
   @override
   void initState() {
     super.initState();
-    selectedGoal = widget.state.goal;
     selectedMinutes = widget.state.dailyMinutes;
   }
 
@@ -72,16 +74,6 @@ class _WelcomePageState extends State<WelcomePage> {
             style: Theme.of(context).textTheme.headlineMedium,
           ),
           const Text('从真实生活场景开始，先做到听得懂、说得清。'),
-          _ChoiceGroup<LearningGoal>(
-            title: '你的主要目标',
-            value: selectedGoal,
-            options: const {
-              LearningGoal.dailyLife: '日常生活',
-              LearningGoal.travel: '旅行',
-              LearningGoal.workStarter: '工作起步',
-            },
-            onChanged: (value) => setState(() => selectedGoal = value),
-          ),
           _ChoiceGroup<int>(
             title: '每天学习多久？',
             value: selectedMinutes,
@@ -91,9 +83,7 @@ class _WelcomePageState extends State<WelcomePage> {
           PrimaryButton(
             label: '继续',
             onPressed: () {
-              widget.state
-                ..setGoal(selectedGoal)
-                ..setDailyMinutes(selectedMinutes);
+              widget.state.setDailyMinutes(selectedMinutes);
               widget.onContinue();
             },
           ),
@@ -119,8 +109,25 @@ class PlacementPage extends StatefulWidget {
   State<PlacementPage> createState() => _PlacementPageState();
 }
 
-class _PlacementPageState extends State<PlacementPage> {
+enum _PlacementPhase { selfReport, listen, readAloud, answer, result }
+
+class _PlacementPageState extends State<PlacementPage>
+    with VoiceAnswerMixin<PlacementPage> {
+  static const _listeningText = 'Hello. My name is Mia. Nice to meet you.';
+  static const _listeningOptions = [
+    '你好，我叫 Mia，很高兴认识你。',
+    '你好，我来自 Mia，今天很开心。',
+    '再见，Mia，明天见。',
+  ];
+  static const _readAloudText = 'Hello. My name is ...';
+
   late PlacementLevel selected;
+  var phase = _PlacementPhase.selfReport;
+  int listeningChoice = -1;
+  final answerController = TextEditingController();
+
+  @override
+  AppState get voiceState => widget.state;
 
   @override
   void initState() {
@@ -128,52 +135,287 @@ class _PlacementPageState extends State<PlacementPage> {
     selected = widget.state.placement;
   }
 
+  @override
+  void dispose() {
+    VoiceService.instance.stopSpeaking();
+    disposeVoiceAnswer(keepRecording: false);
+    answerController.dispose();
+    super.dispose();
+  }
+
+  bool get _understoodGreeting => listeningChoice == 0;
+
+  bool get _answeredName =>
+      coreItemUsedIn('A0-P01', answerController.text.trim());
+
+  /// Placement only picks an A0 starting point until A1 content is frozen, and
+  /// it never marks a lesson as passed.
+  String get _suggestedLessonId =>
+      _understoodGreeting && _answeredName ? 'a0-02' : 'a0-01';
+
+  String get _reason => _understoodGreeting && _answeredName
+      ? '你已经能听懂问候，也能说出自己的名字，可以从拼写名字开始。'
+      : _understoodGreeting
+      ? '你能听懂问候，先把自我介绍说完整会更稳。'
+      : '先从问候和介绍名字开始，打好第一句的基础。';
+
+  void _back() {
+    VoiceService.instance.stopSpeaking();
+    switch (phase) {
+      case _PlacementPhase.selfReport:
+        widget.onBack?.call();
+      case _PlacementPhase.listen:
+        setState(() => phase = _PlacementPhase.selfReport);
+      case _PlacementPhase.readAloud:
+        setState(() => phase = _PlacementPhase.listen);
+      case _PlacementPhase.answer:
+        setState(() => phase = _PlacementPhase.readAloud);
+      case _PlacementPhase.result:
+        setState(() => phase = _PlacementPhase.answer);
+    }
+  }
+
+  void _startFrom(String lessonId) {
+    widget.state.setPlacementStartLesson(lessonId);
+    widget.onStart();
+  }
+
+  Future<void> _toggleVoiceAnswer() async {
+    if (aiVoiceRecording) {
+      await finishVoiceInput(
+        keepAudio: false,
+        onTranscript: (text) => answerController.text = text,
+      );
+      return;
+    }
+    await startVoiceInput();
+  }
+
   @override
   Widget build(BuildContext context) {
+    final showBack =
+        widget.onBack != null || phase != _PlacementPhase.selfReport;
+    return AppPage(
+      appBar: showBack
+          ? AppBar(
+              leading: IconButton(
+                icon: const Icon(Icons.arrow_back),
+                tooltip: "返回",
+                onPressed: _back,
+              ),
+              title: const Text("基础定位"),
+            )
+          : null,
+      child: switch (phase) {
+        _PlacementPhase.selfReport => _selfReport(context),
+        _PlacementPhase.listen => _listen(context),
+        _PlacementPhase.readAloud => _readAloud(context),
+        _PlacementPhase.answer => _answer(context),
+        _PlacementPhase.result => _result(context),
+      },
+    );
+  }
+
+  Widget _selfReport(BuildContext context) {
     const labels = {
       PlacementLevel.beginner: ('完全零基础', '从你好、自我介绍开始'),
       PlacementLevel.someBasics: ('能说一点', '认识常见单词或短句'),
       PlacementLevel.simpleConversation: ('能简单对话', '想说得更自然、更有信心'),
     };
-    return AppPage(
-      appBar: widget.onBack != null
-          ? AppBar(
-              leading: IconButton(
-                icon: const Icon(Icons.arrow_back),
-                tooltip: "返回",
-                onPressed: widget.onBack,
-              ),
-              title: const Text("基础定位"),
-            )
-          : null,
-      child: SpacedColumn(
-        spacing: 14,
-        children: [
-          const Eyebrow('第一步 · 约 3 分钟'),
-          Text('从哪里开始？', style: Theme.of(context).textTheme.headlineMedium),
-          const Text('选择最接近的状态，之后随时能调整。'),
-          for (final option in PlacementLevel.values)
-            _PlacementChoice(
-              option: option,
-              labels: labels[option]!,
-              isSelected: selected == option,
-              onTap: () => setState(() => selected = option),
-            ),
-          PrimaryButton(
-            label: '开始 3 分钟定位',
-            onPressed: () {
-              widget.state.setPlacement(selected);
-              widget.onStart();
-            },
+    return SpacedColumn(
+      spacing: 14,
+      children: [
+        const Eyebrow('第一步 · 约 3 分钟'),
+        Text('从哪里开始？', style: Theme.of(context).textTheme.headlineMedium),
+        const Text('选择最接近的状态，之后随时能调整。'),
+        for (final option in PlacementLevel.values)
+          _PlacementChoice(
+            option: option,
+            labels: labels[option]!,
+            isSelected: selected == option,
+            onTap: () => setState(() => selected = option),
           ),
+        PrimaryButton(
+          label: '开始 3 分钟定位',
+          onPressed: () {
+            widget.state.setPlacement(selected);
+            setState(() => phase = _PlacementPhase.listen);
+          },
+        ),
+        Center(
+          child: TextButton(
+            onPressed: () => _startFrom('a0-01'),
+            child: const Text('直接从第一课开始'),
+          ),
+        ),
+      ],
+    );
+  }
+
+  Widget _listen(BuildContext context) => SpacedColumn(
+    spacing: 14,
+    children: [
+      const Eyebrow('定位 · 1 / 3'),
+      Text('听一听，选出意思。', style: Theme.of(context).textTheme.headlineMedium),
+      SecondaryButton(
+        label: '播放句子',
+        onPressed: () => VoiceService.instance.speak(_listeningText),
+      ),
+      for (var index = 0; index < _listeningOptions.length; index++)
+        SectionCard(
+          tint: listeningChoice == index ? AppColors.softGreen : null,
+          onTap: () => setState(() => listeningChoice = index),
+          child: Row(
+            children: [
+              Icon(
+                listeningChoice == index
+                    ? Icons.radio_button_checked
+                    : Icons.radio_button_off,
+                color: listeningChoice == index
+                    ? AppColors.green
+                    : AppColors.muted,
+              ),
+              const SizedBox(width: 10),
+              Expanded(child: Text(_listeningOptions[index])),
+            ],
+          ),
+        ),
+      PrimaryButton(
+        label: '下一题',
+        onPressed: listeningChoice < 0
+            ? null
+            : () => setState(() => phase = _PlacementPhase.readAloud),
+      ),
+      Center(
+        child: TextButton(
+          onPressed: () => setState(() {
+            listeningChoice = -1;
+            phase = _PlacementPhase.readAloud;
+          }),
+          child: const Text('听不懂，下一题'),
+        ),
+      ),
+    ],
+  );
+
+  Widget _readAloud(BuildContext context) => SpacedColumn(
+    spacing: 14,
+    children: [
+      const Eyebrow('定位 · 2 / 3'),
+      Text('跟着读一句。', style: Theme.of(context).textTheme.headlineMedium),
+      const Text(
+        _readAloudText,
+        textAlign: TextAlign.center,
+        style: TextStyle(fontSize: 26, fontWeight: FontWeight.w600),
+      ),
+      SecondaryButton(
+        label: '播放示范音',
+        onPressed: () => VoiceService.instance.speak(_readAloudText),
+      ),
+      const SectionCard(
+        tint: AppColors.surfaceMuted,
+        child: Text('这一题只是开口热身，不录音、不打分，可以跳过。'),
+      ),
+      PrimaryButton(
+        label: '我读完了',
+        onPressed: () => setState(() => phase = _PlacementPhase.answer),
+      ),
+      Center(
+        child: TextButton(
+          onPressed: () => setState(() => phase = _PlacementPhase.answer),
+          child: const Text('现在不方便开口，跳过'),
+        ),
+      ),
+    ],
+  );
+
+  Widget _answer(BuildContext context) => SpacedColumn(
+    spacing: 14,
+    children: [
+      const Eyebrow('定位 · 3 / 3'),
+      Text('回答这个问题。', style: Theme.of(context).textTheme.headlineMedium),
+      SectionCard(
+        tint: AppColors.surfaceMuted,
+        child: Row(
+          children: [
+            const Expanded(
+              child: Text(
+                'What is your name?',
+                style: TextStyle(fontSize: 20, fontWeight: FontWeight.w600),
+              ),
+            ),
+            IconButton(
+              tooltip: '播放问题',
+              icon: const Icon(Icons.volume_up_outlined),
+              onPressed: () =>
+                  VoiceService.instance.speak('What is your name?'),
+            ),
+          ],
+        ),
+      ),
+      TextField(
+        controller: answerController,
+        decoration: const InputDecoration(hintText: '用英语输入你的回答'),
+        onChanged: (_) => setState(() {}),
+      ),
+      SecondaryButton(
+        label: transcribing ? '正在识别…' : (aiVoiceRecording ? '说完了，识别' : '用语音回答'),
+        onPressed: transcribing ? null : _toggleVoiceAnswer,
+      ),
+      PrimaryButton(
+        label: '查看建议',
+        onPressed: aiVoiceRecording || transcribing
+            ? null
+            : () => setState(() => phase = _PlacementPhase.result),
+      ),
+      Center(
+        child: TextButton(
+          onPressed: () => setState(() {
+            answerController.clear();
+            phase = _PlacementPhase.result;
+          }),
+          child: const Text('还不会说，查看建议'),
+        ),
+      ),
+    ],
+  );
+
+  Widget _result(BuildContext context) {
+    final lesson = lessonById(_suggestedLessonId);
+    return SpacedColumn(
+      spacing: 14,
+      children: [
+        const Eyebrow('定位结果'),
+        Text(
+          '建议从 A0 第 ${lesson.number} 课开始',
+          style: Theme.of(context).textTheme.headlineMedium,
+        ),
+        SectionCard(
+          tint: AppColors.softGreen,
+          child: SpacedColumn(
+            spacing: 6,
+            children: [
+              Text(
+                '第 ${lesson.number} 课 · ${lesson.title}',
+                style: const TextStyle(fontWeight: FontWeight.w600),
+              ),
+              Text(_reason),
+            ],
+          ),
+        ),
+        const Text('前面的课程随时可以回去学，定位不会跳过任何复习。'),
+        PrimaryButton(
+          label: '开始今天学习',
+          onPressed: () => _startFrom(_suggestedLessonId),
+        ),
+        if (_suggestedLessonId != 'a0-01')
           Center(
             child: TextButton(
-              onPressed: widget.onStart,
-              child: const Text('直接从第一课开始'),
+              onPressed: () => _startFrom('a0-01'),
+              child: const Text('从更简单内容开始'),
             ),
           ),
-        ],
-      ),
+      ],
     );
   }
 }