8th: data card documents metadata/credit + metadata/subject/type

Update data card: package-root-relative paths, CC BY full-text/citation, measured-data notes, placeholder feature-table dims

Add pointer to the raw source data archive (RyoMurakami/OpenH-RF-eSAF-raw)

Sync data card: fix stale Data Validation section (zea API reconstruct.py), target description, rotation_angles_deg path

Update data card: corrected eSAF gain stats and known-issues notes

Add README.md