fix(installer): honor WHISPER_PORT override in macOS health probe

[patil2001]

Summary

The macOS installer's Whisper health probe hardcoded port 9000 even when the
installer reassigned WHISPER_PORT to 9100 (AirPlay conflict) or the operator
overrode it in .env, falsely failing the install. The probe now resolves the
port like the STT pre-download and readiness summary do.

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.