Removes user-facing engine/model/key/beam controls. The server now picks
the best available engine automatically:
1. Microsoft Azure Speech — short clips (≤1MB, no diarization, audio/*)
2. Google Cloud Speech v2 — long audio, diarization, all languages
3. OpenAI Whisper GPU — local fallback
Results display which provider was used (e.g. "Transcribed with Google
Cloud Speech") via transcript-engine-badge and traceMeta.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
