feat: collapsible hierarchical category tags + category sort for shelf

- Backend: add parent_category param (matches '历史-*' sub-categories),
  sort=category mode (ORDER BY category ASC), return category_tree with
  parent→sub→count hierarchy
- Frontend: replace flat 63-tag list with collapsible parent tags showing
  book counts, click parent to expand sub-category pills with fade-in
  animation, click sub to filter to exact category
- Add '分类排序' toggle button: when active, books are grouped by
  category with colored section headers showing category name + count
- Clicking same parent again collapses it; '全部' resets everything
- Mobile responsive: smaller tag sizes, reduced indent on narrow screens

app.py

@@ -504,17 +504,21 @@ def api_shelf(conn):
         page (int): 页码，默认 1
         per_page (int): 每页数量，默认 60
         keyword (str): 书名或作者搜索（模糊匹配）
-        category (str): 分类筛选（精确匹配分类名）
+        category (str): 分类筛选（精确匹配完整分类名，如 "历史-中国古代"）
+        parent_category (str): 父分类筛选（如 "历史" 匹配所有 "历史-*" 子分类）
         finished (str): "1" 表示只看已读完
+        sort (str): "category" 表示按分类排序，其他默认按置顶+阅读时间
 
     Returns:
-        JSON: {books: [...], total, page, per_page, total_pages, categories: [...]}
+        JSON: {books: [...], total, page, per_page, total_pages, categories: [...], category_tree: {...}}
     """
     page = int(request.args.get("page", 1))
     per_page = int(request.args.get("per_page", 60))
     keyword = request.args.get("keyword", "").strip()
     category = request.args.get("category", "").strip()
+    parent_category = request.args.get("parent_category", "").strip()
     finished_only = request.args.get("finished", "0") == "1"
+    sort_mode = request.args.get("sort", "").strip()
 
     offset = (page - 1) * per_page
     cursor = conn.cursor()
@@ -528,6 +532,9 @@ def api_shelf(conn):
     if category:
         where_clauses.append("category = %s")
         params.append(category)
+    if parent_category:
+        where_clauses.append("(category = %s OR category LIKE %s)")
+        params.extend([parent_category, f"{parent_category}-%"])
     if finished_only:
         where_clauses.append("finish_reading=1")
 
@@ -537,16 +544,40 @@ def api_shelf(conn):
     cursor.execute(f"SELECT COUNT(*) AS cnt FROM books{where_sql}", params)
     total = cursor.fetchone()["cnt"]
 
-    # 查询当前页数据（置顶优先，最近阅读时间倒序）
+    # 排序
+    if sort_mode == "category":
+        order_sql = " ORDER BY category ASC, is_top DESC, read_update_time DESC"
+    else:
+        order_sql = " ORDER BY is_top DESC, read_update_time DESC"
+
+    # 查询当前页数据
     cursor.execute(
-        f"SELECT * FROM books{where_sql} ORDER BY is_top DESC, read_update_time DESC LIMIT %s OFFSET %s",
+        f"SELECT * FROM books{where_sql}{order_sql} LIMIT %s OFFSET %s",
         params + [per_page, offset],
     )
     rows = cursor.fetchall()
 
-    # 获取所有分类列表（用于前端筛选下拉框）
-    cursor.execute("SELECT DISTINCT category FROM books WHERE category != '' ORDER BY category")
-    categories = [r["category"] for r in cursor.fetchall()]
+    # 获取所有分类列表及层级树
+    cursor.execute(
+        "SELECT category, COUNT(*) AS cnt FROM books "
+        "WHERE category IS NOT NULL AND category != '' "
+        "GROUP BY category ORDER BY category"
+    )
+    cat_rows = cursor.fetchall()
+
+    # 构建层级树: { "历史": {"count": 114, "subs": {"世界史": 5, "中国古代": 10, ...}}, ... }
+    category_tree = {}
+    for r in cat_rows:
+        parts = r["category"].split("-", 1)
+        parent = parts[0]
+        sub = parts[1] if len(parts) > 1 else ""
+        if parent not in category_tree:
+            category_tree[parent] = {"count": 0, "subs": {}}
+        category_tree[parent]["count"] += r["cnt"]
+        if sub:
+            category_tree[parent]["subs"][sub] = r["cnt"]
+
+    categories = [r["category"] for r in cat_rows]
 
     books = []
     for row in rows:
@@ -570,6 +601,7 @@ def api_shelf(conn):
         "per_page": per_page,
         "total_pages": (total + per_page - 1) // per_page,
         "categories": categories,
+        "category_tree": category_tree,
     })