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/lesson/lesson_flow.dart

@@ -38,6 +38,10 @@ class _LessonFlowState extends State<LessonFlow> {
   final writingController = TextEditingController();
   final independentController = TextEditingController();
   int selectedAnswer = -1;
+
+  /// Set once a wrong meaning is picked, so only a first-try choice counts as
+  /// recognition evidence.
+  bool listeningMissed = false;
   int previewIndex = 0;
   bool listeningAudioPlayed = false;
   bool showWritingHelp = true;
@@ -108,7 +112,12 @@ class _LessonFlowState extends State<LessonFlow> {
           correctAnswer: activity.answers.first,
           selectedAnswer: selectedAnswer,
           audioPlayed: listeningAudioPlayed,
-          onSelected: (value) => setState(() => selectedAnswer = value),
+          onSelected: (value) => setState(() {
+            selectedAnswer = value;
+            if (listeningOptions[value] != activity.answers.first) {
+              listeningMissed = true;
+            }
+          }),
           onPlayed: () => setState(() => listeningAudioPlayed = true),
           onLookup: () => showLexiconLookup(
             context,
@@ -118,7 +127,8 @@ class _LessonFlowState extends State<LessonFlow> {
           onContinue:
               selectedAnswer >= 0 &&
                   listeningOptions[selectedAnswer] == activity.answers.first
-              ? widget.state.completeListening
+              ? () =>
+                    widget.state.completeListening(recognized: !listeningMissed)
               : null,
         );
       case LessonStep.speaking:
@@ -126,7 +136,7 @@ class _LessonFlowState extends State<LessonFlow> {
           state: widget.state,
           text: activity.speaking,
           keepRecording: widget.state.keepRecordings,
-          onContinue: () => widget.state.completeSpeaking(assisted: true),
+          onContinue: widget.state.completeSpeaking,
         );
       case LessonStep.reading:
         content = _ReadingStep(