Add Yak Shave Delegation pattern

[devill]

Summary

• Adds new pattern: Yak Shave Delegation - spawn a separate agent for tangential environment/tooling issues instead of breaking flow
• A specific application of the Background Agent pattern focused on unplanned infrastructure distractions
• Adds relationships: uses background-agent, uses focused-agent, solves distracted-agent

Test plan

• npm run validate passes
• npm run build succeeds

🤖 Generated with Claude Code

[emilybache]

Thanks Ivett, this is better than my version of the same thing. I suggest adding the example with rake from my version of it to clarify. I think your overall description is better.