GT derivability repairs (bsb-004 dates, bsb-005 canonical descriptions, bsb-002 continuation lines), refreshed previews, submission instructions

Reissue bsb-004 (522f8c9c): corrected statement PDF, metadata, README, preview

List data/*.pdf and data/metadata.jsonl explicitly: PdfFolder builder with metadata joined

Scope dataset resolution to data/ via data_dir so the viewer joins metadata.jsonl and ignores assets/

Omit manual configs block so the Hub resolves metadata.jsonl; scope challenge counts to released statements

Initial release: 5 statements, metadata, card

initial commit