Add GPUI HTTP client and background gRPC tasks
Introduce ReqwestHttpClient to bridge tokio/reqwest and GPUI's executor
Spawn a tokio runtime in Controller and start background gRPC
stream/tasks (client.rs) to sync tracks, queue, status and images
Change Track model: id is now String; add album_id, artist_id and
optional album_art, plus ArtistImages map
Add UI art components to fetch covers over HTTP and wire the
ReqwestHttpClient into Application
Bump gpui deps (futures, http, reqwest) and add generated API module