Update docs/quickstart.md to use correct CLI command signatures:
- Replace 'cleveragents plan --project' with 'cleveragents plan use <action> --project'
- Replace 'cleveragents apply --project' with 'cleveragents plan list' + 'cleveragents plan apply <plan-id>'
Addresses reviewer non-blocking suggestion to verify CLI commands match
actual signatures before merging.