feat(slackbot): add Claude Code behavior triage skill

[zzstoatzz]

Summary

• add a repo-local Claude Code project skill for classifying Prefect behavior as expected behavior, docs gap, or likely bug
• wire the slackbot research subagent to load project skills and allow the Skill tool
• align the subagent working directory and research cache with the Slackbot example root

Validation

• uv run python -m py_compile examples/slackbot/src/slackbot/research_agent.py
• claude -p --setting-sources project --allowed-tools Skill,Read --model claude-haiku-4-5-20251001 "Is there a project skill named prefect-behavior-triage available in this workspace? If yes, answer yes and summarize when to use it in one sentence. If no, answer no."