feat: add mosaic gateway CLI commands and admin token auth
Gateway daemon lifecycle management via the Mosaic CLI:
- install, start, stop, restart, status, config, logs, uninstall
- Admin API token auth (Bearer tokens) alongside existing session auth
- Bootstrap endpoint for first-user setup (POST /api/bootstrap/setup)
- admin_tokens table in DB schema with SHA-256 hashed tokens
- Gateway .env fallback loading from ~/.config/mosaic/gateway/.env
- CLI daemon management with PID file, log tailing, health checks
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>