- Change default FEATURE_TAILSCALE from NO to YES
- Add build-time warning if TAILSCALE_AUTHKEY not set
- Update firstboot wizard: Tailscale moves to screen 2
- Add summary screen showing Tailscale status
- Update shell-tailscale.sh to handle missing auth key gracefully
- Update BUILD.md with new recommended/optional flow
User experience:
- With auth key: Tailscale auto-connects (secure)
- Without auth key: Warning shown, build continues (public SSH)
- Wizard allows enabling/disabling with clear warnings
No breaking changes - existing builds still work.