[feat]: ENG-2697 use printed webui URL in skill guidance

Update ByteRover skill docs to avoid hardcoded localhost:7700 links now that brv webui resolves the active port.

- point post-curate and onboarding guidance to the URL printed by brv webui
- document brv webui --port <port> for port conflicts or custom ports
- add skill connector regression coverage to reject fixed Web UI localhost URLs