Polish item 1 (option A): add page-level source_url per poll row (verified Wikipedia opinion-polling page); README note; datapackage/croissant/CHECKSUMS/DATASHEET regenerated (Frictionless).

Gold-standard cheap layer v1.1.0: datapackage.json (Frictionless, validated), croissant.json (MLCommons), CHECKSUMS.txt (SHA-256), DATASHEET.md (Gebru). Additive; data unchanged.