Coordinator mode: new guidance to load a skill before briefing workers

In coordinator mode, one Claude directs separate worker agents that do the actual work. There is new guidance text for that mode. It tells the coordinator to do two things before briefing a worker on a task that a listed skill covers, or before replying about that work:

• Load the skill read-only with its skill tool. A skill is a packaged set of instructions.
• Put "Use the / skill" in the worker's prompt, "because only workers execute skills".

The guidance is added only in this case:

• CLAUDE_CODE_COORDINATOR_SKILL_GUIDANCE is set. It is an environment variable, meaning a setting passed to Claude Code from your shell.
• The coordinator's list of tools includes the skill tool.