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/components/Files.tsx

@@ -34,6 +34,7 @@ import { MoreButton } from "./ui/MoreButton";
 import NavGrid from "./ui/NavGrid";
 import Overlay from "./ui/Overlay";
 import { PageToolbar } from "./ui/PageShell";
+import { LinkBox } from "./LinkBox";
 import Pager from "./ui/Pager";
 import { Pressable } from "./ui/Pressable";
 import { LoadingState, StateMessage } from "./ui/QueryState";
@@ -572,9 +573,8 @@ export default function Files() {
               {t("files.count", { count: rows.length })}
             </span>
           )}
-          {/* Wraps on a phone: sort, view and Upload together are wider than the column. */}
-          <span className="ml-auto flex min-w-0 flex-wrap items-center justify-end gap-2">
-            {isGrid && (
+          {isGrid && (
+            <span className="ml-auto">
               <ColumnSortControl
                 columns={columns}
                 sort={sort}
@@ -584,23 +584,31 @@ export default function Files() {
                 ascLabel={t("files.sort.asc")}
                 descLabel={t("files.sort.desc")}
               />
-            )}
-            <ViewSwitcher
-              value={layout}
-              options={layoutOptions}
-              onChange={(next) => setLayouts({ ...layouts, [viewKey]: next })}
-              label={t("files.layout.label")}
-            />
-            {canUpload && (
-              <Button
-                variant="outline"
-                size="sm"
-                icon={<UploadCloud className="w-4 h-4" />}
-                onClick={() => setUpload({ file: null })}
-              >
-                {t("files.actions.upload")}
-              </Button>
-            )}
+            </span>
+          )}
+          {/* The intake row (DESIGN.md "Files page"): paste a link, or upload; then the paint. On a
+              phone the link box takes the line and the rest wraps under it. A link is downloaded
+              into its site's folder whatever is open, so the box stays even in Shared with me. */}
+          <span className="flex w-full flex-wrap items-center gap-2">
+            <LinkBox className="flex-[1_1_18rem]" />
+            <span className="ml-auto flex items-center gap-2">
+              {canUpload && (
+                <Button
+                  variant="outline"
+                  size="sm"
+                  icon={<UploadCloud className="w-4 h-4" />}
+                  onClick={() => setUpload({ file: null })}
+                >
+                  {t("files.actions.upload")}
+                </Button>
+              )}
+              <ViewSwitcher
+                value={layout}
+                options={layoutOptions}
+                onChange={(next) => setLayouts({ ...layouts, [viewKey]: next })}
+                label={t("files.layout.label")}
+              />
+            </span>
           </span>
         </div>
       </PageToolbar>