fix(server,web): forward-fix CI lint + vitest failures

- gofmt -s on system.go, system_cron.go, api.go
- rename unused r → _ in 3 fetcher_test.go HTTP handlers
- TrackRow +queue test uses /add .* to queue/i (track-aware aria-label from #377)
- /library/artists page test mocks likes + tanstack-query (ArtistCard now embeds LikeButton)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/components/TrackRow.test.ts

@@ -95,7 +95,7 @@ describe('TrackRow', () => {
 
   test('+ queue button calls enqueueTrack and does NOT trigger row play', async () => {
     render(TrackRow, { props: { tracks, index: 0 } });
-    await fireEvent.click(screen.getByRole('button', { name: /add to queue/i }));
+    await fireEvent.click(screen.getByRole('button', { name: /add .* to queue/i }));
     expect(enqueueTrack).toHaveBeenCalledWith(tracks[0]);
     expect(playQueue).not.toHaveBeenCalled();
   });