fix: speed up lifecycle transitions

[aserper]

Summary

• cache qmd availability and collection checks for 5 minutes to avoid repeated subprocess work during reloads
• skip exit summary generation on lifecycle transitions by default (/reload, /new, /resume, /fork)
• add PI_MEMORY_SUMMARIZE_TRANSITIONS=1 opt-in for users who prefer summaries during those transitions
• add a regression test for qmd status/collection caching and transition-summary config

Validation

• npm run build
• npm run lint
• npx tsx test/qmd-cache.ts
• commit hook also ran npm test: 6 passed, 0 failed, 5 skipped

Context

In local profiling, repeated qmd status and qmd collection list --json calls dominated /reload time. Caching these checks and avoiding summary/qmd-update work on lifecycle transitions keeps reload/new responsive while preserving the old transition-summary behavior behind an env var.

[jayzeng]

@aserper thanks for the PR, can you resolve the merge conflict?

[aserper]

fixed

[jayzeng]

I cherry picked your changes and resolved the merge conflicts, PR here: #16