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.

backend/app/routes/downloads.py

@@ -842,6 +842,7 @@ def admin_list_downloads(
     out = []
     for j in jobs:
         data = serialize(j, assets.get(j.asset_id) if j.asset_id is not None else None)
+        data["user_id"] = j.user_id
         data["user_email"] = emails.get(j.user_id)
         out.append(data)
     return out
@@ -860,19 +861,35 @@ def admin_storage(admin: User = Depends(admin_user), db: Session = Depends(get_d
         .where(DownloadJob.asset_id.is_not(None))
         .group_by(DownloadJob.user_id)
     ).all()
-    emails = {
-        u.id: u.email
-        for u in db.execute(select(User).where(User.id.in_([uid for uid, _ in per_user]))).scalars()
+    uids = [uid for uid, _ in per_user]
+    emails = {u.id: u.email for u in db.execute(select(User).where(User.id.in_(uids))).scalars()}
+    # What each one's Files lists: their finished files.
+    files: dict[int, int] = {
+        uid: n
+        for uid, n in db.execute(
+            select(DownloadJob.user_id, func.count())
+            .where(DownloadJob.user_id.in_(uids), DownloadJob.status == JobStatus.DONE)
+            .group_by(DownloadJob.user_id)
+        ).tuples()
     }
+
+    def row(uid: int) -> dict:
+        lim = quota.resolve(db, uid)
+        return {
+            "user_id": uid,
+            "email": emails.get(uid),
+            "footprint_bytes": quota.footprint(db, uid),
+            "files": files.get(uid, 0),
+            "max_bytes": lim.max_bytes,
+            "unlimited": lim.unlimited,
+        }
+
     return {
         "files_on_disk": on_disk[0],
         "total_bytes": int(on_disk[1]),
         "total_assets": total_assets,
         "total_cap_bytes": sysconfig.get_int(db, "download_total_max_bytes"),
-        "per_user": [
-            {"user_id": uid, "email": emails.get(uid), "footprint_bytes": quota.footprint(db, uid)}
-            for uid, _ in per_user
-        ],
+        "per_user": [row(uid) for uid in uids],
     }