R1: Boot config banner + eager validation + health-wait progress beacons #10

Three pgbus-pattern DX improvements:

• Boot/deploy config banner echoing effective proxy config incl. "loadbalancer auto-enabled (primary role has N hosts)" — the 2026-07-03 auto-LB surprise would have been visible (pgbus#213).
• Eager config validation before any ssh connection (pgbus#215).
• Progress beacons during health-check waits (elapsed/attempts instead of 30s of silence) (pgbus#222).

Verify: deploy output shows the banner and periodic beacons; invalid config fails before ssh.