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/test/review_feedback_test.dart

@@ -1,4 +1,5 @@
 import 'package:flutter_test/flutter_test.dart';
+import 'package:kouyu_english/core/a0_core.dart';
 import 'package:kouyu_english/core/models.dart';
 import 'package:kouyu_english/core/review_feedback.dart';
 
@@ -99,11 +100,35 @@ void main() {
     );
     // Multi-space on word item
     expect(
-      ReviewFeedback.check(
-        review('A0-W08', 'three'),
-        '   THREE   ',
-      ).complete,
+      ReviewFeedback.check(review('A0-W08', 'three'), '   THREE   ').complete,
       isTrue,
     );
   });
+
+  test('a dictation review needs the whole sentence that was played', () {
+    final item = review('A0-W24', 'water').copyWith(
+      skill: dictationSkill,
+      prompt: coreReviewVariant('A0-W24', 1).prompt,
+    );
+    expect(ReviewFeedback.check(item, 'water').complete, isFalse);
+    expect(ReviewFeedback.check(item, 'I like watter.').complete, isFalse);
+    expect(ReviewFeedback.check(item, 'i like water').complete, isTrue);
+  });
+
+  test('offline review variants rotate recall, dictation and speaking', () {
+    expect(coreReviewVariant('A0-P12', 0).skill, '回忆表达');
+    expect(coreReviewVariant('A0-P12', 1).skill, dictationSkill);
+    expect(coreReviewVariant('A0-P12', 2).skill, spokenRecallSkill);
+    expect(coreReviewVariant('A0-P12', 3).skill, '回忆表达');
+    for (final id in a0CoreItems.keys) {
+      final sentence = a0DictationSentences[id];
+      expect(sentence, isNotNull, reason: id);
+      // Each dictation sentence really contains the item it checks.
+      expect(
+        coreItemUsedIn(id, sentence!.sentence, word: a0CoreItems[id]),
+        isTrue,
+        reason: id,
+      );
+    }
+  });
 }