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.

frontend/src/components/UploadDialog.tsx

@@ -10,7 +10,7 @@ import { isAborted } from "../lib/api/core";
 import { notifyActionError } from "../lib/actionErrors";
 import { invalidateDownloads } from "../lib/downloads";
 import { notify } from "../lib/notifications";
-import { navigateTo } from "../lib/nav";
+import { showInTray } from "../lib/downloadQueue";
 import type { DownloadJob } from "../lib/api";
 import { useFilesActions } from "./filesContext";
 import { formatBytes } from "../lib/format";
@@ -68,11 +68,10 @@ export default function UploadDialog({
   // same reason, and `formAlerts.dom.test.tsx` is the test that exists because of it.
   const [pickSeq, setPickSeq] = useState(0);
   const { openFile } = useFilesActions();
-  // A done file is in Files, opened on it; one the worker still converts is in the download queue
-  // until it is.
+  // A done file is in Files, opened on it; one the worker still converts is in the tray until it is.
   const openUploaded = (job: DownloadJob) => {
     if (job.status === "done") openFile(job.id, job.folder_id ?? null);
-    else navigateTo("downloads");
+    else showInTray(job.id);
   };
   const pick_ = (f: File) => {
     setFile(f);