feat(schema): v0.6.0 — PSA backfill migration + Yoast-integrated Drug/MedicalWebPage/FAQ schema
Piece 1 — Backfill migration 0004: copies PSA psa_molecular_formula/weight/aliases
into PR Core _pr_* meta. Idempotent + re-runnable. PubChem REST fallback for 4
posts missing PSA data (MAX_RETRIES=3, exp backoff). All PSA values UNTRUSTED.
PR_CORE_TARGET_SCHEMA_VERSION bumped 3 -> 4.
Piece 2 — Drug node enrichment + stable @id = {permalink}#drug (ratified contract).
Reads _pr_* schema-input meta. molecularWeight in g/mol. Empty-prop guard throughout.
Piece 3 — Yoast-integrated emission via wpseo_schema_graph_pieces (priority 11),
wpseo_schema_webpage_type (MedicalWebPage retype), wpseo_schema_graph (enrichment).
Standalone @graph fallback retained. No duplicate WebPage/BreadcrumbList.
FAQPage emitted only when _pr_faq_items populated.
Supporting: PR_Core_Schema_Sanitizers, PR_Core_Pubchem_Client, CONTEXT.md,
ARCHITECTURE.md, CONVENTIONS.md, CHANGELOG.md, uninstall.php purge.
Tests: test-migration-0004.php (20 assertions), test-jsonld.php (29 assertions).
Agent-Session: peptide-schema-backfill v0.6.0
1e5999e663