feat(admin): unify dashboard + login design with landing/docs theme

feat(providers): prefix-based routing with per-model custom aliases

feat(dashboard): refine admin dashboard UI

feat(dashboard): update admin dashboard UI

fix(admin): display model names instead of IDs in dashboard models list

fix(admin): prevent infinite reload loop on 401

Upload folder using huggingface_hub

feat(admin): add IP-bound API key manager + gpt-image-2 endpoint

refactor: extract HTML templates to separate files