- Add inline API key input to each provider (expand via key icon, save/replace keys from the GUI)
- Rename "General" section to "Configure Defaults" for clarity
- Remove confusing separate Diarization toggle — auto-couple with output format selection (matches CLI behavior)
- Backend transcribe route now auto-promotes output_format to "diarized" when diarize=true (matching CLI)
- Bump version to v0.7.4.1

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>