feat(onboard): add node onboarding scaffold (bash, idempotent)
- scripts/onboard/onboard.sh: orchestrator with --node/--step/--from/--dry-run flags,
deploy_autonomy + git_control gates, lexicographic step ordering
- scripts/onboard/lib/common.sh: log/warn/die/step helpers, yaml_get (yq+grep/sed fallback),
ensure_line, git() wrapper enforcing --no-pager
- scripts/onboard/lib/remote.sh: rrun/rcopy/rsync_dir/rcheck SSH wrappers, dry-run aware
- scripts/onboard/steps/00-preflight.sh: read-only fact collection (arch, RAM, disk, docker,
tailscale, MagicMirror runtime, swap), human report + machine YAML snippet
- scripts/onboard/steps/10-50: stub files with TODO headers, no mutations
- hosts/lustro/node.yaml: LUSTRO edge node draft (KEN, role=edge, deploy_autonomy=true,
git_control=false); hardware fields marked TODO for preflight population
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>