Add endpoints for browsing, downloading, and deleting dicts hosted on
HuggingFace. Manifest is fetched and cached from the remote repo to
show available dicts with download status and version comparison.
- /dicts/remote GET: list available dicts from HF manifest
- /dicts/{name}/download POST: download dict from HF with atomic write
- /dicts/{name} DELETE: remove local copy and evict cache
- ItemDictRemote model with downloaded/update_available flags
- Exclude manifest.json from local dict listing in all scan paths