Spec 37: Conditional chunk loading

[noahbfreedman-cloud]

Summary

• add frontmatter and config-driven conditional chunk loading rules
• apply conditional filtering in the hook pre-task path
• add a CLI for listing, checking, and explaining chunk conditions

Testing

• python3 -m pytest tests/test_conditions.py tests/test_hooks.py tests/test_chunk_defaults.py tests/test_keywords_cli.py -q