Enhance extract_metadata() with three new optional fields for page-aware chunking support. Validates list length mismatches. Fully backward compatible — existing callers unaffected.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
Woody