feat(files): the Downloads page goes — the tray, a Storage tab and a Downloads settings tab take its place

- The Downloads module, its rail icon and badge are gone. A bookmark, the remembered page and an old
  history entry that name it land on Files (urlState.resolvePage); `g d` goes to Files too.
- Users page: a Storage tab — the disk in numbers, every user's use against their own limit with
  their file count, every user's downloads; aligned tables, one menu per row (edit / reset quota,
  open source, copy, the owner's quota). The admin storage rows carry quota + file count, the admin
  job list its owner.
- Settings: a Downloads tab — the download formats in one list (duplicate a built-in, edit or delete
  your own) and the site sign-ins, moved from Account.
- "View" on an added download, a clip or a converting upload opens the tray on that row (unfolded,
  back if closed; a finished one opens as a file; under a player it opens without taking focus).
- The download dialog opens on the format used last.
- DataTable: `pager={false}` for a short list, `cardRow` to give a lone "…" its own card line.
- Welcome and README speak of Files; a new Files screenshot.

CLAUDE.md

@@ -5,7 +5,7 @@ be developed that way. This file is the rules of the road: read it before you to
 loaded into every agent session, so keep it **short and true**. A rule here that has gone stale is
 worse than no rule — if you change how the code works, change this file in the same commit.
 
-Siftlode is a self-hosted YouTube reader (+ a local Plex browser/player and a download center). It is a
+Siftlode is a self-hosted YouTube reader (+ a local Plex browser/player and a files library with downloads). It is a
 **modular monolith**: one Postgres, one FastAPI process (uvicorn + APScheduler), one worker process
 (yt-dlp/ffmpeg), one PO-token sidecar. React 19 (with the React Compiler) + react-query frontend, with a
 router-free navigation provider.