Add offline MP3 rendering, Game Boy styling for UX test, fix 16-bit → 8-bit

- Add renderOffline() to SynthesisEngine for faster-than-realtime audio rendering
- Add renderOffline() to MotifEngine wrapping the synthesis engine
- Update ux-test.html MP3 download to use offline rendering (no more real-time capture)
- Restyle ux-test.html with Game Boy LCD aesthetic to match main site
- Fix "16-Bit" to "8-Bit" across all titles and share cards (Game Boy is 8-bit!)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/src/server.ts

@@ -220,7 +220,7 @@ app.get('/s/:code', async (req, res) => {
     const imageUrl = origin ? `${origin}/warioX.png` : '/warioX.png';
 
     const sharedTitle = (payload.title || '').trim();
-    const ogTitle = sharedTitle ? `${sharedTitle} - Wario Synth` : 'Wario Synth 16-Bit Midi';
+    const ogTitle = sharedTitle ? `${sharedTitle} - Wario Synth` : 'Wario Synth 8-Bit Midi';
     const ogDescription = sharedTitle
       ? `I made ${sharedTitle} Game Boy version. Click to listen or generate your own.`
       : 'Turn any song into a Game Boy version';