feat(downloads): S1 UI quick wins — queue default, dates, auto-link, thumb fallback

- Always land on the Queue tab (drop the persisted last-tab) so new work/failures are the default view
- Show the download date (relative) on Library rows
- Share dialog opens with a default link already generated when none exists; all link controls stay available
- Thumbnail falls back to the self-hosted poster when a remote (i.ytimg/fbcdn) thumbnail 404s
- Add a clipboard-paste affordance to the add-URL box (explicit button + best-effort on focus)

frontend/src/components/ShareDialog.tsx

@@ -1,4 +1,4 @@
-import { useMemo, useState } from "react";
+import { useEffect, useMemo, useRef, useState } from "react";
 import { qk } from "../lib/queryKeys";
 import { useTranslation } from "react-i18next";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
@@ -271,6 +271,18 @@ function LinkShare({ job }: { job: DownloadJob }) {
     },
   });
 
+  // Open with a link already generated: sharing is almost always the goal, so mint a default
+  // (no password, no expiry, view-only) link the moment the dialog finds none — as if the user
+  // had pressed "New link" → "Create". All further controls (password, download toggle, expiry,
+  // extra links, revoke) stay available on the created link and via the "New link" button.
+  const autoTried = useRef(false);
+  useEffect(() => {
+    if (links.data && links.data.length === 0 && !autoTried.current && !create.isPending) {
+      autoTried.current = true;
+      create.mutate();
+    }
+  }, [links.data, create]);
+
   return (
     <div>
       <div className="flex items-center gap-2 text-sm font-medium mb-1">
@@ -282,7 +294,7 @@ function LinkShare({ job }: { job: DownloadJob }) {
         {(links.data ?? []).map((l) => (
           <LinkRow key={l.id} link={l} onChanged={invalidate} />
         ))}
-        {links.data && links.data.length === 0 && !creating && (
+        {links.data && links.data.length === 0 && !creating && !create.isPending && (
           <p className="text-xs text-muted">{t("downloads.share.noLinks")}</p>
         )}
       </div>