feat: add book detail, notes detail, recommendation page and MySQL schema

新增功能：
- 书籍详情弹窗：点击书架书籍展示详细信息（书名、作者、出版社、ISBN、字数、评分、简介、阅读进度），数据实时从微信读书 API 获取并入库
- 笔记详情弹窗：点击有笔记的书展示划线和想法/点评，按章节分组展示，数据实时获取并入库
- 推荐页面：个性化推荐（为你推荐）+ 关键词搜索书籍，数据从微信读书 API 获取并入库
- 修复 Flask 中文 URL 参数编码问题

后端新增 API：
- GET /api/book/detail?book_id=xxx — 书籍详情
- GET /api/book/notes?book_id=xxx — 笔记详情（划线+想法）
- GET /api/recommend?maxIdx=0 — 个性化推荐
- GET /api/search?keyword=xxx — 搜索书籍

数据库新增表：
- book_details, book_progress, book_highlights, book_chapters
- book_reviews, recommended_books, search_results

MySQL 版本建表语句 schema_mysql.sql：
- 18 张表的完整 DDL，含索引、字符集 utf8mb4、字段注释
- 适用于后续从 SQLite 迁移至 MySQL

templates/index.html

@@ -21,6 +21,7 @@
                 <a href="#top-books" class="nav-link">读书排行</a>
                 <a href="#shelf" class="nav-link">书架</a>
                 <a href="#notes" class="nav-link">笔记</a>
+                <a href="#discover" class="nav-link">推荐</a>
             </div>
             <div class="nav-update" id="fetchTime"></div>
         </div>
@@ -117,6 +118,49 @@
         </div>
     </section>
 
+    <!-- 推荐发现 -->
+    <section id="discover" class="discover-section">
+        <div class="container">
+            <h2 class="section-title">🔍 推荐发现</h2>
+            <div class="discover-tabs">
+                <button class="discover-tab active" id="tabRecommend" onclick="switchDiscoverTab('recommend')">为你推荐</button>
+                <button class="discover-tab" id="tabSearch" onclick="switchDiscoverTab('search')">搜索书籍</button>
+            </div>
+            <!-- 推荐区 -->
+            <div id="recommendPanel" class="discover-panel">
+                <div class="discover-controls">
+                    <button class="btn-primary" onclick="loadRecommend(0)">刷新推荐</button>
+                    <button class="btn-secondary" onclick="loadMoreRecommend()">换一批</button>
+                </div>
+                <div class="discover-grid" id="recommendGrid"></div>
+            </div>
+            <!-- 搜索区 -->
+            <div id="searchPanel" class="discover-panel" style="display:none">
+                <div class="search-box">
+                    <input type="text" id="searchInput" class="search-input" placeholder="输入书名、作者或关键词..." onkeydown="if(event.key==='Enter')doSearch()">
+                    <button class="btn-primary" onclick="doSearch()">搜索</button>
+                </div>
+                <div class="discover-grid" id="searchGrid"></div>
+            </div>
+        </div>
+    </section>
+
+    <!-- 书籍详情弹窗 -->
+    <div class="modal-overlay" id="bookDetailModal" onclick="closeModal('bookDetailModal')">
+        <div class="modal-content book-detail-modal" onclick="event.stopPropagation()">
+            <span class="modal-close" onclick="closeModal('bookDetailModal')">&times;</span>
+            <div id="bookDetailBody" class="modal-body"></div>
+        </div>
+    </div>
+
+    <!-- 笔记详情弹窗 -->
+    <div class="modal-overlay" id="notesDetailModal" onclick="closeModal('notesDetailModal')">
+        <div class="modal-content notes-detail-modal" onclick="event.stopPropagation()">
+            <span class="modal-close" onclick="closeModal('notesDetailModal')">&times;</span>
+            <div id="notesDetailBody" class="modal-body"></div>
+        </div>
+    </div>
+
     <!-- 页脚 -->
     <footer class="footer">
         <div class="container">