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/home/home_page.dart

@@ -12,12 +12,16 @@ class HomePage extends StatelessWidget {
     required this.onStartPrimaryTask,
     required this.onOpenDialogue,
     required this.onResumeLessonDialogue,
+    required this.onStartReinforcement,
+    required this.onOpenAssessment,
   });
 
   final AppState state;
   final VoidCallback onStartPrimaryTask;
   final VoidCallback onOpenDialogue;
   final VoidCallback onResumeLessonDialogue;
+  final VoidCallback onStartReinforcement;
+  final ValueChanged<String> onOpenAssessment;
 
   @override
   Widget build(BuildContext context) {
@@ -26,16 +30,21 @@ class HomePage extends StatelessWidget {
     final activeLesson = lessonById(state.activeLessonId);
     final activeSegment = state.activeSegmentIndexFor(activeLesson.id) + 1;
     final resumeDialogue = state.hasResumableLessonDialogue;
+    final stageStep = !resumeDialogue && !isReview && state.allLessonsComplete
+        ? _stageStep()
+        : null;
     final primaryTitle = resumeDialogue
         ? '继续第 ${activeLesson.number} 课的课程对话'
         : isReview
         ? '先复习 $count 项'
-        : '第 ${activeLesson.number} 课 · ${activeLesson.title}${activeLesson.segments.length > 1 ? ' · 第 $activeSegment/${activeLesson.segments.length} 段' : ''}';
+        : stageStep?.title ??
+              '第 ${activeLesson.number} 课 · ${activeLesson.title}${activeLesson.segments.length > 1 ? ' · 第 $activeSegment/${activeLesson.segments.length} 段' : ''}';
     final primaryNote = resumeDialogue
         ? '已保留你的对话进度和提示状态。'
         : isReview
         ? (state.reviewBacklog ? '有积压项目；先花几分钟清掉到期复习。' : '昨天练过的关键句，今天换个情境再用一次。')
-        : '预热词汇 → 听说读写 → 对话 → 独立尝试';
+        : stageStep?.note ?? '预热词汇 → 听说读写 → 对话 → 独立尝试';
+    final scene = state.recommendedScene;
 
     return AppPage(
       child: SpacedColumn(
@@ -80,7 +89,9 @@ class HomePage extends StatelessWidget {
                       ),
                     ),
                     Text(
-                      isReview ? '${(count * 2).clamp(2, 10)} 分钟' : '12 分钟',
+                      isReview
+                          ? '${(count * 2).clamp(2, 10)} 分钟'
+                          : stageStep?.minutes ?? '12 分钟',
                       style: const TextStyle(color: AppColors.green),
                     ),
                   ],
@@ -94,10 +105,10 @@ class HomePage extends StatelessWidget {
                       ? '继续对话'
                       : isReview
                       ? '开始复习'
-                      : '开始今天的学习',
+                      : stageStep?.action ?? '开始今天的学习',
                   onPressed: resumeDialogue
                       ? onResumeLessonDialogue
-                      : onStartPrimaryTask,
+                      : stageStep?.onPressed ?? onStartPrimaryTask,
                 ),
               ],
             ),
@@ -110,7 +121,7 @@ class HomePage extends StatelessWidget {
                   style: TextStyle(fontSize: 16, fontWeight: FontWeight.w600),
                 ),
                 Text(
-                  '初次见面 · 4 个任务 · 文字或语音输入',
+                  '${scene.title} · ${scene.script.prompts.length} 个任务 · 文字或语音输入',
                   style: Theme.of(context).textTheme.bodyMedium,
                 ),
                 SecondaryButton(label: '开始情境对话', onPressed: onOpenDialogue),
@@ -122,6 +133,56 @@ class HomePage extends StatelessWidget {
       ),
     );
   }
+
+  /// What comes after the last A0 lesson: consolidation until the core items
+  /// are ready, then the stage assessment, then waiting for A1 content.
+  _StageStep _stageStep() {
+    final usable =
+        '可使用 ${state.coreUsableCount}/48 · 已掌握 ${state.coreMasteredCount}/30';
+    if (state.a0Passed) {
+      return _StageStep(
+        title: 'A0 已通过',
+        note: 'A1 课程准备中。先用巩固练习和情境对话保持手感。',
+        action: '安排一题巩固练习',
+        minutes: '3 分钟',
+        onPressed: onStartReinforcement,
+      );
+    }
+    final packId = state.nextAssessmentPackId;
+    if (state.a0AssessmentReady && packId != null) {
+      return _StageStep(
+        title: 'A0 阶段评估 · $packId',
+        note: '$usable。可以开始阶段评估，两套评估间隔至少 24 小时。',
+        action: '开始阶段评估',
+        minutes: '15 分钟',
+        onPressed: () => onOpenAssessment(packId),
+      );
+    }
+    return _StageStep(
+      title: state.a0AssessmentReady ? '第二套评估 24 小时后开放' : 'A0 课程已学完',
+      note: state.a0AssessmentReady
+          ? '第一套评估已通过。等待期间继续巩固。'
+          : '$usable。继续按时复习、做情境对话，达到要求后开放阶段评估。',
+      action: '安排一题巩固练习',
+      minutes: '3 分钟',
+      onPressed: onStartReinforcement,
+    );
+  }
+}
+
+class _StageStep {
+  const _StageStep({
+    required this.title,
+    required this.note,
+    required this.action,
+    required this.minutes,
+    required this.onPressed,
+  });
+  final String title;
+  final String note;
+  final String action;
+  final String minutes;
+  final VoidCallback onPressed;
 }
 
 class _FrameworkNote extends StatelessWidget {