- Implement `ReactionService` to manage file reactions in the database.
- Add `POST /d/{boxID}/f/{fileID}/react` endpoint to handle user reactions.
- Add `GET /emoji/{pack}/{file}` endpoint to serve custom emoji assets.
- Support loading custom emoji packs dynamically from the data directory.
- Update README with instructions on configuring emoji reaction packs.
Modify the authentication handler to return an unauthorized error when
an invalid or disabled bearer token is provided, rather than silently
falling back to an anonymous request.
This ensures that clients attempting to authenticate but failing (due to
expired, malformed, or disabled tokens) are explicitly notified of the
auth failure instead of proceeding anonymously. True anonymous requests
without any Authorization header remain supported.
