fix(health): do not fail host-network services on port check

[patil2001]

Summary

health-check.sh always ran the port probe even for host_network services (port 0), so enabling tailscale made ods health report DEGRADED for a healthy stack. test_service now skips the port check for host-network services per the service-registry contract.

AI Assistance

AI-assisted; reviewed and verified locally before opening.

Release Lane

• Stable hotfix targeting release/2.6.x
• Mainline change targeting main
• Next-minor work targeting the next feature/minor release
• Not sure; reviewer should help classify

Changed Surface

• Docs only
• Tests only
• Dashboard UI
• Dashboard API / host agent
• Installer / bootstrap / lifecycle
• Docker Compose / service manifests
• Model routing / Hermes / capabilities
• Network exposure / auth / proxy
• Dependencies / runtime wiring

Risk And Validation

• Risk level: Low
• Validation run:
  • git diff --check
  • Not required because: narrow change; syntax and diff checks pass locally

Commands/results:

git diff --check clean; bash -n on touched scripts passes

Operational Change Check

• This is an operational change and validation is recorded above.