Clean up API documentation files by removing Phase X references:
Remove 'API Explorer will be inserted here in Phase X' placeholders from:
- 70+ API endpoint documentation files
- Authentication endpoints (login, logout, register, refresh)
- User endpoints (profile, settings, password)
- Device endpoints (registration, sync, shelves)
- Library endpoints (CRUD, folders, visibility)
- Media endpoints (items, progress, highlights, notes)
- Admin endpoints (users, analytics)
- Sync endpoints (Kobo, KOReader)
- OPDS endpoints
- Scanner endpoints
- Queue endpoints
These placeholders were from planning documents and have no meaning
to API consumers. The documentation is now clean and ready for use.
- Update api-reference.md with new endpoint paths
- Update api-reference.md Books API section → Media Items API section
- Update index.md Books API link → Media Items API
- Update get_shelf.md cover_url reference from /api/books/ to /api/media-items/