Complete rewrite of /library page to match Notion's Library design:
1. Table view with columns: Page name (with icon), Created by (avatar),
Source, Last edited time, Last visited time
2. Hover effects showing drag handle (6 dots), checkbox, OPEN button
3. Side peek panel: opens on right, shows page content preview,
close button, favorite toggle, copy link, more menu
4. Multi-selection: checkbox per row, select-all header, 'X selected' bar
with Delete and '...' menu
5. ... menu: Remove from Recents, Copy links to all, Move to, Move to Trash
6. Inline rename: double-click title → edit field
7. 6 tabs: Recents, Favorites, Shared, Published, Private, Workspace
8. Tree expand/collapse for nested pages (has_children support)
9. + Add new row at bottom
10. Search bar toggleable
API additions:
- library.py: enhanced _build_item with icon, source_label, author
- dashboard.py: new /api/pages/{id}/content, /rename, /trash endpoints
- All 133 tests pass