studia_bas — Studia BAS policy articles (scoped from #19)

Replacement delivery for the studia_bas contribution in #19 (authored by @gzawadzki — this account cannot push to refs/pr/19: "Forbidden to push on refs/pr/19", same author-scoped ref policy as #24). This PR carries only the source; the shared build_dynaword.py change is split out into the companion flags PR, per review item 2.

This PR: data/studia_bas/* (112 articles / 2,256,009 cl100k_base tokens / 6,089,085 chars, CC-BY-3.0-PL), src/fetch_studia_bas.py, src/audit_studia_bas.py, src/report_studia_bas_audit.py, src/test_audit_studia_bas.py, src/test_studia_bas_contract.py, the registry entry (added: 2026-07-19, release: None) and the source_findings.md entry.

Companion PR: build_dynaword.py preserve_id / preserve_created opt-in flags + test_build_dynaword_flags.py + .gitignore tooling lines — reviewable independently. Order of merge is free; a rebuild through build_dynaword.py needs both (the entry flags are inert without the flags PR). The committed shard is already built.

Review items from #19:

1. PII — the datasheet now states which scrubber ran: scrub_pii() in src/fetch_studia_bas.py (regex pass: e-mail, ORCID, labelled PESEL/NIP/REGON, labelled phone -> [PII]), plus structural exclusion of author-affiliation/contact blocks and ORCID values at extraction. Not NERGAL — the shard must be re-run through SlayerLab/NERGAL before release (quoted case material and third-party names can survive any regex pass); merge with release: None is fine meanwhile. The existing audit (src/audit_studia_bas.py: 0 structured residuals across all 115 extracted records) is evidence for the current build, not a substitute.
2. Split — done (this PR + the companion flags PR).
3. Rebase — the source sits on main @ 34e7ea3 in one clean commit; no shared-file drift.

The source's own documentation is unchanged otherwise: per-article DOI/attribution/PDF-hash sidecar for CC BY attribution, Crossref-verified coverage (issues 66–82, zero missing journal-articles), per-PDF CC BY 3.0 PL license statements verified 17/17.

Verification: python3 -m pytest src/test_studia_bas_contract.py src/test_audit_studia_bas.py — passed on the clean tree; python3 -m pytest src/test_build_dynaword_flags.py — 3 passed on the companion PR.