Fix dit-vae cover mode: remove unsupported CLI flags

[Copilot]

Cover mode jobs were failing because the spawn-mode code passed --reference-audio, --repainting-start, and --repainting-end to dit-vae — none of which exist in the binary. Only --src-audio is supported for audio input.

Changes

• server/src/services/acestep.ts
  • Remove --reference-audio push (caused Unknown option crash on every cover job)
  • Remove --repainting-start / --repainting-end pushes (not yet implemented in dit-vae; roadmap items)
  • Retain the existing --src-audio for sourceAudioUrl — the correct and only supported audio-input flag

- if (params.referenceAudioUrl)  ditArgs.push('--reference-audio', resolveAudioPath(params.referenceAudioUrl));
- if (params.sourceAudioUrl)     ditArgs.push('--src-audio',       resolveAudioPath(params.sourceAudioUrl));
- if (params.repaintingStart && params.repaintingStart > 0)
-                                ditArgs.push('--repainting-start', String(params.repaintingStart));
- if (params.repaintingEnd && params.repaintingEnd > 0)
-                                ditArgs.push('--repainting-end',   String(params.repaintingEnd));
+ if (params.sourceAudioUrl) ditArgs.push('--src-audio', resolveAudioPath(params.sourceAudioUrl));

Reference audio and repainting will be wired up in follow-on PRs once the binary supports them.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.