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/core/speech_compare.dart

@@ -0,0 +1,149 @@
+/// 把设备转写和示范句逐词对照。这不是发音评分：转写只说明“机器听成了什么”，
+/// 用来提示学习者哪些词没被听出来，值得再听示范、再说一次。
+class SpokenWord {
+  const SpokenWord(this.text, {required this.heard});
+
+  /// 示范句中的原词（保留大小写和标点，便于直接显示）。
+  final String text;
+  final bool heard;
+}
+
+class SpokenComparison {
+  const SpokenComparison({required this.words, required this.extraWords});
+
+  final List<SpokenWord> words;
+
+  /// 转写里出现、但示范句没有的词。
+  final List<String> extraWords;
+
+  int get heardCount => words.where((word) => word.heard).length;
+  int get total => words.length;
+  List<String> get missedWords => [
+    for (final word in words)
+      if (!word.heard) word.text,
+  ];
+
+  /// 全部听出且没有多余词。
+  bool get matches => total > 0 && heardCount == total && extraWords.isEmpty;
+
+  /// 大部分词被听出（≥ 80%）。
+  bool get close => total > 0 && heardCount / total >= 0.8;
+}
+
+const _digitWords = [
+  'zero',
+  'one',
+  'two',
+  'three',
+  'four',
+  'five',
+  'six',
+  'seven',
+  'eight',
+  'nine',
+];
+
+const _contractions = {
+  "i'm": ['i', 'am'],
+  "it's": ['it', 'is'],
+  "what's": ['what', 'is'],
+  "that's": ['that', 'is'],
+  "he's": ['he', 'is'],
+  "she's": ['she', 'is'],
+  "name's": ['name', 'is'],
+  "don't": ['do', 'not'],
+  "you're": ['you', 'are'],
+};
+
+/// 一个显示词对应的比较单位。例如 "I’m" 展开为 i/am，"138" 展开为
+/// one/three/eight，"o’clock" 统一为 oclock。
+List<String> _unitsOf(String raw) {
+  var word = raw
+      .toLowerCase()
+      .replaceAll(RegExp(r'[‘’`´]'), "'")
+      .replaceAll(RegExp(r"[^a-z0-9']"), '');
+  word = word.replaceAll(RegExp(r"^'+|'+$"), '');
+  if (word.isEmpty) return const [];
+  if (word == "o'clock") return const ['oclock'];
+  final expanded = _contractions[word];
+  if (expanded != null) return expanded;
+  if (RegExp(r'^\d+$').hasMatch(word)) {
+    return [for (final digit in word.split('')) _digitWords[int.parse(digit)]];
+  }
+  return [word.replaceAll("'", '')];
+}
+
+List<String> _displayWords(String text) => text
+    .replaceAll(RegExp(r'[-–—/]'), ' ')
+    .split(RegExp(r'\s+'))
+    .where((word) => _unitsOf(word).isNotEmpty)
+    .toList();
+
+List<String> _heardUnits(String transcript) => [
+  for (final word in _displayWords(transcript)) ..._unitsOf(word),
+];
+
+SpokenComparison compareSpoken(String expected, String transcript) {
+  final display = _displayWords(expected);
+  final expectedUnits = <String>[];
+  final owner = <int>[];
+  for (var index = 0; index < display.length; index++) {
+    for (final unit in _unitsOf(display[index])) {
+      expectedUnits.add(unit);
+      owner.add(index);
+    }
+  }
+  var heard = _heardUnits(transcript);
+  // 拼读时转写常把字母连成一个词（S H E N → Shen），拆回单个字母。
+  final spellsLetters =
+      expectedUnits.isNotEmpty &&
+      expectedUnits.every((unit) => RegExp(r'^[a-z]$').hasMatch(unit));
+  if (spellsLetters) {
+    heard = [for (final unit in heard) ...unit.split('')];
+  }
+
+  // 最长公共子序列：保持词序，重复词也能正确对齐。
+  final n = expectedUnits.length;
+  final m = heard.length;
+  final table = List.generate(n + 1, (_) => List.filled(m + 1, 0));
+  for (var i = n - 1; i >= 0; i--) {
+    for (var j = m - 1; j >= 0; j--) {
+      table[i][j] = expectedUnits[i] == heard[j]
+          ? table[i + 1][j + 1] + 1
+          : (table[i + 1][j] >= table[i][j + 1]
+                ? table[i + 1][j]
+                : table[i][j + 1]);
+    }
+  }
+  final unitHeard = List.filled(n, false);
+  final heardUsed = List.filled(m, false);
+  var i = 0;
+  var j = 0;
+  while (i < n && j < m) {
+    if (expectedUnits[i] == heard[j]) {
+      unitHeard[i] = true;
+      heardUsed[j] = true;
+      i++;
+      j++;
+    } else if (table[i + 1][j] >= table[i][j + 1]) {
+      i++;
+    } else {
+      j++;
+    }
+  }
+
+  final wordHeard = List.filled(display.length, true);
+  for (var unit = 0; unit < n; unit++) {
+    if (!unitHeard[unit]) wordHeard[owner[unit]] = false;
+  }
+  return SpokenComparison(
+    words: [
+      for (var index = 0; index < display.length; index++)
+        SpokenWord(display[index], heard: wordHeard[index]),
+    ],
+    extraWords: [
+      for (var index = 0; index < m; index++)
+        if (!heardUsed[index]) heard[index],
+    ],
+  );
+}