fix: top-bar indicator links to downloads when download/task is active

Previously it always linked to /discovery. Now it links to /downloads
when there are active downloads or tasks, and /discovery only when
discovery is the sole thing running.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/Layout.jsx

@@ -129,10 +129,12 @@ function DownloadIndicator() {
     );
   }
 
+  const indicatorTarget = (activeDownloads.length || tasks.length) ? "/downloads" : "/discovery";
+
   return (
     <div className="relative group shrink-0">
       <Link
-        to="/discovery"
+        to={indicatorTarget}
         className="flex items-center gap-1.5 px-2 py-1 rounded-lg bg-zinc-800 hover:bg-zinc-700 transition-colors text-xs text-zinc-300"
       >
         <svg className="w-3 h-3 animate-spin text-zinc-400 shrink-0" fill="none" viewBox="0 0 24 24">