feat(design): a library row keeps Share (the link copy) in sight, ahead of save (E28 S3e3)

The owner's call: sharing a download's link is the library's main errand, more
important than saving the file, so it does not hide in the row's "…". Manage
sharing stays in the menu. The "…" tests press as a mouse, so a stray long-press
timer no longer fires after teardown.

frontend/src/components/DownloadCenter.tsx

@@ -10,6 +10,7 @@ import {
   PlayCircle,
   Plus,
   Settings2,
+  Share2,
   UploadCloud,
 } from "lucide-react";
 import Tabs from "./ui/Tabs";
@@ -259,6 +260,10 @@ export default function DownloadCenter() {
                       <PlayCircle className="w-4 h-4" />
                     </IconBtn>
                   )}
+                  {/* Sharing the link is the library's main errand: in sight, ahead of save. */}
+                  <IconBtn onClick={() => actions.share(job)} title={t("downloads.actions.share")}>
+                    <Share2 className="w-4 h-4" />
+                  </IconBtn>
                   {saveBtn(job)}
                 </DownloadRow>
               ))}