Model Downloader

The headline local-first card a user sees while a model loads on-device: model name, size, context length, category, a live progress bar, and a clear first-time-downloading vs loading-from-cache distinction (with a ready state). Includes a lower-level DownloadProgress (bar + percentage from a 0–1 fraction or {loaded,total,percent,cached}). Presentational — bind progress to useModelLoader/useModelStatus; it does not own the download. Lifted out of a chat empty-state into a reusable primitive.