fix: 25s backend timeout + 30s frontend timeout on Spotify resolve

Extracts resolve logic into _resolveSpotify() and wraps it in
Promise.race with a 25s timer so the backend always sends a response
even if undici's AbortSignal.timeout silently fails on blocked sockets.
Also reduces frontend timeout from 90s to 30s.

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

src/spotify.js

@@ -63,7 +63,7 @@ export async function resolveSpotifyLink() {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
       body: JSON.stringify({ url }),
-      signal: AbortSignal.timeout(90000),
+      signal: AbortSignal.timeout(30000),
     });
     if (!res.ok) {
       const err = await res.json().catch(() => ({}));