feat: A1 短材料复现本单元理解词，并加入黑夜模式

课程内容
- 重写全部 21 个 A1 单元的听读材料，把本单元理解词织进听/读文本，
  单元内理解词复现率从约 20% 提升到约 77%（各单元 56–96%）。
- 修正 U01 房间号与机场大巴同为 thirty 的撞车（改为 17/30/40）。
- 校验器容差按级别读取（A1 为 8%），materials 覆盖率、字数、
  选项子串等校验全部通过；course_content_test 通过。

黑夜模式
- app_theme 拆分明/暗两套调色板，AppColors 随亮度切换；
  main 用 theme/darkTheme/themeMode + builder 镜像已解析亮度；
  主题偏好持久化到快照；进度页新增“外观主题”切换。

文档
- COURSE-PACK-JSON.md 更新 A1 词池覆盖（840/933）与材料复现约定。

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

kouyu_english/lib/features/lesson/steps/independent_step.dart

@@ -190,7 +190,7 @@ class _IndependentStepState extends State<_IndependentStep>
             tint: AppColors.warm,
             child: Text(
               validationError!,
-              style: const TextStyle(color: AppColors.warmInk),
+              style: TextStyle(color: AppColors.warmInk),
             ),
           ),
         if (!widget.showHelp)

kouyu_english/lib/features/lesson/steps/listening_step.dart

@@ -8,6 +8,7 @@ class _ListeningStep extends StatelessWidget {
     required this.correctAnswer,
     required this.selectedAnswer,
     required this.audioPlayed,
+    required this.missed,
     required this.onSelected,
     required this.onPlayed,
     required this.onLookup,
@@ -21,6 +22,9 @@ class _ListeningStep extends StatelessWidget {
 
   final int selectedAnswer;
   final bool audioPlayed;
+
+  /// 选错过或查看过原文；此后可以看原文，但本题不再算独立听辨。
+  final bool missed;
   final ValueChanged<int> onSelected;
   final VoidCallback onPlayed;
   final VoidCallback onLookup;
@@ -29,6 +33,9 @@ class _ListeningStep extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final answers = options;
+    final answeredCorrectly =
+        selectedAnswer >= 0 && answers[selectedAnswer] == correctAnswer;
+    final revealText = answeredCorrectly || missed;
     return _LessonScaffold(
       step: 2,
       child: SpacedColumn(
@@ -47,22 +54,23 @@ class _ListeningStep extends StatelessWidget {
               onPlayed: onPlayed,
             ),
           ),
-          TextButton.icon(
-            onPressed: onLookup,
-            icon: const Icon(Icons.menu_book_outlined),
-            label: const Text('查看词或短语'),
-          ),
-          if (audioPlayed)
-            SectionCard(child: LexiconText(activity.listening, state: state)),
+          if (!audioPlayed)
+            Text(
+              '先播放音频，听完再选择。原文会在作答后显示。',
+              style: TextStyle(color: AppColors.muted),
+            ),
+          if (revealText)
+            SectionCard(child: LexiconText(activity.listening, state: state))
+          else if (audioPlayed)
+            TextButton.icon(
+              onPressed: onLookup,
+              icon: const Icon(Icons.menu_book_outlined),
+              label: const Text('听不懂，查看原文和词义（本题不计入听辨）'),
+            ),
           for (var index = 0; index < answers.length; index++)
             SectionCard(
               tint: selectedAnswer == index ? AppColors.softGreen : null,
-              onTap: () {
-                onSelected(index);
-                if (!audioPlayed) {
-                  onPlayed();
-                }
-              },
+              onTap: audioPlayed ? () => onSelected(index) : null,
               child: Row(
                 children: [
                   Icon(
@@ -74,18 +82,23 @@ class _ListeningStep extends StatelessWidget {
                         : AppColors.muted,
                   ),
                   const SizedBox(width: 10),
-                  Text(answers[index]),
+                  Text(
+                    answers[index],
+                    style: audioPlayed
+                        ? null
+                        : TextStyle(color: AppColors.muted),
+                  ),
                 ],
               ),
             ),
           PrimaryButton(
             label: selectedAnswer >= 0
                 ? '检查并继续'
-                : (audioPlayed ? '请选择答案' : '先播放音频或选择答案'),
+                : (audioPlayed ? '请选择答案' : '先播放音频'),
             onPressed: onContinue,
           ),
           if (selectedAnswer >= 0 && answers[selectedAnswer] != correctAnswer)
-            const Text(
+            Text(
               '再听一次，选择正确答案。',
               style: TextStyle(color: AppColors.warmInk),
             ),

kouyu_english/lib/features/lesson/steps/reading_step.dart

@@ -95,7 +95,7 @@ class _ReadingStepState extends State<_ReadingStep> {
                 Row(
                   mainAxisAlignment: MainAxisAlignment.spaceBetween,
                   children: [
-                    const Row(
+                    Row(
                       children: [
                         Icon(
                           Icons.chat_bubble_outline,
@@ -117,7 +117,7 @@ class _ReadingStepState extends State<_ReadingStep> {
                       onTap: () =>
                           VoiceService.instance.speak(widget.activity.reading),
                       borderRadius: BorderRadius.circular(16),
-                      child: const Padding(
+                      child: Padding(
                         padding: EdgeInsets.symmetric(
                           horizontal: 8,
                           vertical: 4,
@@ -194,7 +194,7 @@ class _ReadingStepState extends State<_ReadingStep> {
                     color: AppColors.green.withValues(alpha: 0.12),
                     borderRadius: BorderRadius.circular(6),
                   ),
-                  child: const Text(
+                  child: Text(
                     '问题',
                     style: TextStyle(
                       color: AppColors.green,
@@ -207,7 +207,7 @@ class _ReadingStepState extends State<_ReadingStep> {
                 Expanded(
                   child: Text(
                     widget.activity.readingQuestion,
-                    style: const TextStyle(
+                    style: TextStyle(
                       fontSize: 15,
                       fontWeight: FontWeight.w600,
                       color: AppColors.ink,
@@ -279,7 +279,7 @@ class _ReadingStepState extends State<_ReadingStep> {
                     color: AppColors.green.withValues(alpha: 0.3),
                   ),
                 ),
-                child: const Row(
+                child: Row(
                   children: [
                     Icon(Icons.check_circle, color: AppColors.green, size: 20),
                     SizedBox(width: 8),
@@ -309,7 +309,7 @@ class _ReadingStepState extends State<_ReadingStep> {
                     color: AppColors.warmInk.withValues(alpha: 0.2),
                   ),
                 ),
-                child: const Row(
+                child: Row(
                   children: [
                     Icon(
                       Icons.help_outline,
@@ -333,7 +333,7 @@ class _ReadingStepState extends State<_ReadingStep> {
             TextField(
               controller: controller,
               onChanged: (_) => setState(() {}),
-              decoration: const InputDecoration(
+              decoration: InputDecoration(
                 hintText: '用英文输入答案',
                 filled: true,
                 fillColor: AppColors.surface,
@@ -346,7 +346,7 @@ class _ReadingStepState extends State<_ReadingStep> {
               tint: AppColors.warm,
               child: Text(
                 '答案：${widget.activity.readingAnswer}',
-                style: const TextStyle(color: AppColors.warmInk),
+                style: TextStyle(color: AppColors.warmInk),
               ),
             ),
           if (!showAnswer &&

kouyu_english/lib/features/lesson/steps/speaking_step.dart

@@ -4,10 +4,12 @@ class _SpeakingStep extends StatefulWidget {
   const _SpeakingStep({
     required this.state,
     required this.text,
+    this.tip = '',
     required this.keepRecording,
     required this.onContinue,
   });
   final String text;
+  final String tip;
   final AppState state;
   final bool keepRecording;
   final VoidCallback onContinue;
@@ -78,21 +80,18 @@ class _SpeakingStepState extends State<_SpeakingStep>
           textAlign: TextAlign.center,
           style: const TextStyle(fontSize: 30, fontWeight: FontWeight.w600),
         ),
-        Text(
-          '/es - eɪtʃ - iː - en/',
-          style: Theme.of(context).textTheme.bodyMedium,
-        ),
         SectionCard(
           tint: AppColors.surfaceMuted,
           child: _AudioRow(label: '播放示范音', speech: widget.text),
         ),
-        const SectionCard(
-          tint: AppColors.warm,
-          child: Text(
-            '字母之间留一个短停顿。先清楚，不必快。',
-            style: TextStyle(color: AppColors.warmInk),
+        if (widget.tip.isNotEmpty)
+          SectionCard(
+            tint: AppColors.warm,
+            child: Text(
+              widget.tip,
+              style: TextStyle(color: AppColors.warmInk),
+            ),
           ),
-        ),
         SecondaryButton(
           label: transcribing
               ? '正在 AI 识别发音…'
@@ -137,9 +136,11 @@ class _SpeakingStepState extends State<_SpeakingStep>
             ),
           ),
         if (transcript.isNotEmpty)
-          SectionCard(child: Text("设备转写：$transcript\n请确认它是否接近你刚才说的内容。")),
+          _SpokenComparisonCard(expected: widget.text, transcript: transcript),
         const SectionCard(
-          child: Text('转写不确定或与原句不符时，可重说或继续文字练习；这一步只算跟读练习，不作为独立口语证据。'),
+          child: Text(
+            '转写只反映机器听成了什么，不等于发音评分；没听出的词可以再听示范、重说一次。这一步只算跟读练习，不作为独立口语证据。',
+          ),
         ),
         PrimaryButton(
           label: transcript.isEmpty ? '我已跟读，继续' : '确认并继续',
@@ -149,3 +150,54 @@ class _SpeakingStepState extends State<_SpeakingStep>
     ),
   );
 }
+
+class _SpokenComparisonCard extends StatelessWidget {
+  const _SpokenComparisonCard({
+    required this.expected,
+    required this.transcript,
+  });
+
+  final String expected;
+  final String transcript;
+
+  @override
+  Widget build(BuildContext context) {
+    final result = compareSpoken(expected, transcript);
+    final summary = result.matches
+        ? '每个词都被听出来了。'
+        : result.close
+        ? '大部分词都被听出来了，橙色的词再练一次。'
+        : '有几个词没被听出来：先听示范，再慢一点说。';
+    return SectionCard(
+      tint: result.close ? AppColors.softGreen : AppColors.warm,
+      child: SpacedColumn(
+        spacing: 8,
+        children: [
+          Text('听出 ${result.heardCount}/${result.total} 个词。$summary'),
+          Wrap(
+            spacing: 6,
+            runSpacing: 6,
+            children: [
+              for (final word in result.words)
+                Text(
+                  word.text,
+                  style: TextStyle(
+                    fontSize: 18,
+                    fontWeight: FontWeight.w600,
+                    color: word.heard ? AppColors.green : AppColors.warmInk,
+                    decoration: word.heard
+                        ? TextDecoration.none
+                        : TextDecoration.underline,
+                  ),
+                ),
+            ],
+          ),
+          Text(
+            '设备转写：$transcript',
+            style: Theme.of(context).textTheme.bodySmall,
+          ),
+        ],
+      ),
+    );
+  }
+}

kouyu_english/lib/features/lesson/steps/writing_step.dart

@@ -152,7 +152,7 @@ class _WritingStepState extends State<_WritingStep> {
                   Text('还可补充：${aiFeedback!.missing.join('、')}'),
                 if (aiFeedback!.suggestion != null)
                   Text('可参考改写：${aiFeedback!.suggestion}'),
-                const Text(
+                Text(
                   '这是学习帮助；请按自己的意思重写后再检查，系统不会仅凭 AI 建议记为掌握。',
                   style: TextStyle(fontSize: 12, color: AppColors.muted),
                 ),
@@ -164,7 +164,7 @@ class _WritingStepState extends State<_WritingStep> {
             tint: AppColors.warm,
             child: Text(
               aiFeedbackError!,
-              style: const TextStyle(color: AppColors.warmInk),
+              style: TextStyle(color: AppColors.warmInk),
             ),
           ),
         if (result != null)