feat(recite): 完成背诵模块基础框架与核心页面开发

本次提交实现了背诵模块的完整基础链路：
1. 新增词书、背单词接口层与对应数据模型
2. 完成背诵首页、章节列表页等核心页面开发
3. 实现音频播放、加载弹窗等通用组件
4. 配置路由跳转链路，替换旧版缓存传参方案
5. 对齐Vue端业务逻辑与UI样式

lib/core/api/lexicon_book/api.dart

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+import 'package:new_learn/core/api/lexicon_book/model.dart';
+import 'package:new_learn/core/network/dio_client.dart';
+
+/// ============================================================
+/// 【lexicon_book 模块接口】词书接口 —— 对标 Vue3 端 api/lexiconBook/index.ts
+///
+///   getCurrentBook  → GET  GetCurrentLexiconBooks   当前学习的词书
+///   getLearnDayCount→ GET  GetLearnDayCount         坚持学习天数
+///   getAllBooks     → GET  GetAllLexiconBooks       我的书库
+///   startLearn      → POST StartLearn/{bookId}      切换/开始学习某书
+///
+/// 说明：Vue 端这 4 个接口都带 hideErrorToast（静默失败），
+/// 异常不在此层吞，交页面按需要 catch 空处理。
+/// ============================================================
+class LexiconBookApi {
+  LexiconBookApi._();
+
+  static final LexiconBookApi instance = LexiconBookApi._();
+
+  /// 后端响应壳 {code, message, data} 统一取 data
+  dynamic _unwrap(dynamic data) =>
+      data is Map<String, dynamic> && data['data'] != null
+      ? data['data']
+      : data;
+
+  /// 当前学习的词书（未选择时后端可能返回 null）
+  Future<BookInfo?> getCurrentBook() async {
+    final data = _unwrap(
+      await DioClient.instance.get('/api/v1/LexiconBook/GetCurrentLexiconBooks'),
+    );
+    if (data is Map<String, dynamic>) return BookInfo.fromJson(data);
+    return null;
+  }
+
+  /// 坚持学习天数
+  Future<int> getLearnDayCount() async {
+    final data = _unwrap(
+      await DioClient.instance.get('/api/v1/LexiconBook/GetLearnDayCount'),
+    );
+    if (data is num) return data.toInt();
+    if (data is String) return int.tryParse(data) ?? 0;
+    return 0;
+  }
+
+  /// 我的书库全部词书
+  Future<List<BookInfo>> getAllBooks() async {
+    final data = _unwrap(
+      await DioClient.instance.get('/api/v1/LexiconBook/GetAllLexiconBooks'),
+    );
+    if (data is List) {
+      return data
+          .whereType<Map<String, dynamic>>()
+          .map(BookInfo.fromJson)
+          .toList();
+    }
+    return const [];
+  }
+
+  /// 切换 / 开始学习某书
+  Future<bool> startLearn(int bookId) async {
+    final data = _unwrap(
+      await DioClient.instance.post(
+        '/api/v1/LexiconBook/StartLearn/$bookId',
+      ),
+    );
+    return data == true;
+  }
+}

lib/core/api/lexicon_book/model.dart

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+/// ============================================================
+/// 【lexicon_book 模块模型】词书实体 —— 对标 Vue3 端 api/lexiconBook/type.ts
+///
+///   BookInfo：词书（背诵首页当前书 / 教材列表我的书库）
+/// ============================================================
+library;
+
+/// 兼容 number | String 的 id 安全转换（对标 TS 的 number | string）
+int _safeId(dynamic v) {
+  if (v is num) return v.toInt();
+  if (v is String) return int.tryParse(v) ?? 0;
+  return 0;
+}
+
+/// 词书信息
+class BookInfo {
+  const BookInfo({
+    this.id = 0,
+    this.title = '',
+    this.cover = '',
+    this.poster = '',
+    this.slogan = '',
+    this.lexiconCount = 0,
+    this.totalCount = 0,
+    this.isStudying = false,
+  });
+
+  final int id;
+  final String title; // 书名
+  final String cover; // 封面图
+  final String poster; // 顶部海报图
+  final String slogan; // 海报标语
+  final int lexiconCount; // 已学词数
+  final int totalCount; // 总词数
+  final bool isStudying; // 是否学习中
+
+  /// 学习进度百分比（0~100，取整；totalCount 为 0 时兜底 0）
+  int get progressPercent =>
+      totalCount <= 0 ? 0 : (lexiconCount * 100 ~/ totalCount);
+
+  factory BookInfo.fromJson(Map<String, dynamic> json) {
+    return BookInfo(
+      id: _safeId(json['id']),
+      title: json['title'] as String? ?? '',
+      cover: json['cover'] as String? ?? '',
+      poster: json['poster'] as String? ?? '',
+      slogan: json['slogan'] as String? ?? '',
+      lexiconCount: (json['lexiconCount'] as num?)?.toInt() ?? 0,
+      totalCount: (json['totalCount'] as num?)?.toInt() ?? 0,
+      isStudying: json['isStudying'] as bool? ?? false,
+    );
+  }
+}