Add VAD-based smart segmentation for long audio

- Integrate NeMoVAD-iOS for voice activity detection
- Return ASRResult with text, segments, and timestamps
- Smart merging of close segments, splitting of long ones
- Update ContentView to display timestamped segments
- Update README with new API documentation

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

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

Release 1.0.0