fix: clean boot — suppress kernel messages + init debug output
- Kernel: quiet loglevel=0 (was loglevel=4)
- Init: remove all echo statements to console
- ac-native stderr redirected to /dev/null (logs go to USB file only)
- Swank starts silently
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>