feat(files): download from anywhere — a link box, a pasted link, the palette; the running downloads in a tray

- Files toolbar link box (paste button, Enter); a lone http(s) link pasted onto any page opens the one
  app-wide download dialog, which now names the link; the palette's "Download from a link…" focuses
  the box on its history entry.
- The download tray, bottom right on every page: what waits, runs, is paused or failed (reason +
  Retry, the queue's right-click / "…" menu), and what finished in this tab as "Done · Open" until
  closed; folds to a pill (per-account pref); closed, it stays shut — across a reload — until the
  work changes or something finishes. Back to top steps up over it, the page end keeps clear.
- A finish is announced once: "Downloaded: …", whether a phone plays it, Copy link + Open (toasts
  and notices may carry a second action).
- The inbox's ready notice opens the file in its folder: download_done carries job_id + folder_id.
- GET /api/downloads is the queue only (in flight, failed, finished in the last 10 minutes), with
  each row's source key.

frontend/src/lib/storage.ts

@@ -21,6 +21,11 @@ export const LS = {
   filesLayouts: "siftlode.filesLayouts",
   filesSort: "siftlode.filesSort",
   filesCardSize: "siftlode.filesCardSize",
+  // The download tray open or folded to its pill — a per-account mirror of the server pref.
+  downloadTray: "siftlode.downloadTray",
+  // The queue the reader closed the tray on (job ids, a failure marked) — it stays shut until that
+  // changes. Per-account mirror of the server pref.
+  downloadTrayClosed: "siftlode.downloadTrayClosed",
   hints: "siftlode.hints",
   lang: "siftlode.lang",
   filters: "siftlode.filters",