html-skills-listen — server-mode setup for html-skills artifacts

System primitive for the html-skills plugin. It runs a bundled script that detects the environment, starts (or finds) this session's local receiver on an ephemeral port, and prints what you need; you then arm a Monitor on the receiver's log so each submit becomes a session notification, and hand the URL back to the skill that invoked you.

Steps

Run the setup script with this session's id:
```
bash "${CLAUDE_PLUGIN_ROOT}/skills/html-skills-listen/scripts/listen.sh" "${CLAUDE_SESSION_ID}"
```
Output is KEY=VALUE lines. Always present: SID, LOG, MIDF, STATUS. With STATUS=STARTED or STATUS=ALREADY_RUNNING you also get URL. After a restart of a receiver that had died, STATUS=STARTED also prints RESTARTED=1 and, if its previous port could not be reused, PORT_CHANGED=1.
Branch on STATUS:
- STATUS=WEB — Claude Code web session; the sandbox can't reach the user's browser. Don't arm a Monitor. Tell the parent skill (or the user, if invoked directly):
  
  ⓘ Claude Code web session detected. Server mode can't work here. The artifact will use clipboard mode automatically — Submit copies JSON to the clipboard for paste-back.