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/shell/learning_shell.dart

@@ -26,6 +26,7 @@ class _LearningShellState extends State<LearningShell> {
   var route = _ShellRoute.tab;
   _ShellRoute? previousRoute;
   bool dialogueInLesson = false;
+  String sceneId = 'a0-meet';
   AssessmentPack? assessmentPack;
   DialogueSummaryData? dialogueSummary;
 
@@ -45,9 +46,10 @@ class _LearningShellState extends State<LearningShell> {
     route = _ShellRoute.scene;
   });
 
-  void showDialogue({bool inLesson = false}) => setState(() {
+  void showDialogue({bool inLesson = false, String? scene}) => setState(() {
     previousRoute = route;
     dialogueInLesson = inLesson;
+    if (scene != null) sceneId = scene;
     route = _ShellRoute.dialogue;
   });
 
@@ -125,13 +127,16 @@ class _LearningShellState extends State<LearningShell> {
         );
       case _ShellRoute.scene:
         body = DialogueScenePage(
-          onStart: showDialogue,
+          state: widget.state,
+          onStart: (id) => showDialogue(scene: id),
           onBack: () => showTab(tab),
         );
       case _ShellRoute.dialogue:
         body = DialoguePage(
+          key: ValueKey(dialogueInLesson ? 'lesson' : 'scene-$sceneId'),
           state: widget.state,
           isLessonDialogue: dialogueInLesson,
+          sceneId: sceneId,
           onFinished: (summary) {
             if (dialogueInLesson) {
               showLesson();
@@ -147,7 +152,7 @@ class _LearningShellState extends State<LearningShell> {
           summary: dialogueSummary!,
           onHome: () => showTab(AppTab.home),
           onLesson: showLesson,
-          onRetry: showDialogue,
+          onRetry: () => showDialogue(scene: sceneId),
           onBack: () => showTab(tab),
         );
       case _ShellRoute.settings:
@@ -194,7 +199,8 @@ class _LearningShellState extends State<LearningShell> {
                   selectedIndex: tab.index,
                   height: 70,
                   indicatorColor: AppColors.softGreen,
-                  onDestinationSelected: (index) => showTab(AppTab.values[index]),
+                  onDestinationSelected: (index) =>
+                      showTab(AppTab.values[index]),
                   destinations: const [
                     NavigationDestination(
                       icon: Icon(Icons.home_outlined),
@@ -243,6 +249,16 @@ class _LearningShellState extends State<LearningShell> {
           },
           onOpenDialogue: showDialogueScene,
           onResumeLessonDialogue: () => showDialogue(inLesson: true),
+          onStartReinforcement: () {
+            widget.state.scheduleA0Reinforcement();
+            showTab(AppTab.review);
+          },
+          onOpenAssessment: (packId) {
+            final pack = a0AssessmentPacks
+                .where((item) => item.id == packId)
+                .firstOrNull;
+            if (pack != null) showAssessment(pack);
+          },
         );
       case AppTab.learn:
         return _LearningMap(
@@ -258,7 +274,10 @@ class _LearningShellState extends State<LearningShell> {
           state: widget.state,
         );
       case AppTab.dialogue:
-        return DialogueScenePage(onStart: showDialogue);
+        return DialogueScenePage(
+          state: widget.state,
+          onStart: (id) => showDialogue(scene: id),
+        );
       case AppTab.review:
         return ReviewPage(
           state: widget.state,