- 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
1. Fix hdCover() to also replace s_ prefix (search results use s_ not t6_)
2. Add persistent search bar below navbar, switches to discover tab on search
3. Shelf search now supports book title and author search (new keyword param)
4. Add category tag pills above book grid, click to filter by category
5. Update /api/shelf backend: keyword param for title/author, category for exact match
6. Mobile responsive styles for search bar and category tags