fix(header): show the sync chip only where it means something, trim its copy

The chip is about YouTube subscription syncing, so it only earns its place on
the feed those subscriptions fill and the manager where you curate them. On
Plex — a different source entirely — plus playlists, downloads and stats it was
just noise.

Its tooltips were written for a roomy sidebar block and read like documentation
on a pill: the counts explanation went 120 chars -> 48, the full-history one
142 -> 46, and pause/resume drop "background".

frontend/src/components/Header.tsx

@@ -120,8 +120,12 @@ export default function Header({
       />
       {search}
       {/* Per-user sync status — it used to cost the nav rail a whole block. It sits with the other
-          pills rather than pinned to the far right: on a wide window that just strands it. */}
-      <SyncStatus isAdmin={me.role === "admin"} onGoToFullHistory={onGoToFullHistory} />
+          pills rather than pinned to the far right: on a wide window that just strands it. Only on
+          the two modules it says anything about: the feed those subscriptions fill, and the manager
+          where you curate them. It's noise on Plex (a different source entirely), playlists, etc. */}
+      {(page === "feed" || page === "channels") && (
+        <SyncStatus isAdmin={me.role === "admin"} onGoToFullHistory={onGoToFullHistory} />
+      )}
     </div>
   );
 }