Replace all orange/red icon assets with new brand colors:
- Circle background #191919, logo mark #FBFAF5
- Regenerated: icon.png, icon.ico, icon.icns, all tray icons
- Updated generate-icons.py with new palette and circle shape
- Added source logo.svg
- Bump version to 0.4.92
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>