fix(jsonld): accept string|array @type — v0.6.1

Yoast's wpseo_schema_webpage_type filter passes ['WebPage'] (array) on
every singular page. The v0.6.0 retype_to_medical_webpage() signature
was strict string, causing TypeError → HTTP 500 on ALL singulars under
strict_types=1. Secondary bug: enrich_webpage_piece compared
'WebPage' === $piece['@type'] but @type is an array, so MedicalWebPage
enrichment never injected.

Fix:
- retype_to_medical_webpage: string|array param + return (PHP 8.1+ union)
- enrich_webpage_piece: normalise @type to array before in_array() check
- Add tests/unit/test-jsonld-webpage.php: regression tests with array
  input for both code paths; fail against v0.6.0, pass after fix
- Bump version header + PR_CORE_VERSION constant to 0.6.1
- CHANGELOG entry under [0.6.1]

Agent-Session: jsonld-webpage-typefix v0.6.1

CHANGELOG.md

@@ -3,6 +3,13 @@
 All notable changes to Peptide Repo Core are documented here.
 Format: [Semantic Versioning](https://semver.org/).
 
+## [0.6.1] — 2026-06-13
+
+### Fixed
+- Fix: Yoast `wpseo_schema_webpage_type` passes `string|array` on singulars — accept `string|array` in `retype_to_medical_webpage()` signature; return type updated to match (PHP 8.1+ union). Eliminates `TypeError` → HTTP 500 on all singular pages (monographs + plain Pages) under `strict_types=1`.
+- Fix: `enrich_webpage_piece` compared `'WebPage' === $piece['@type']` but Yoast sets `@type` as an array on singular pages. Normalise `@type` to array before `in_array()` check; `lastReviewed`, `reviewedBy`, and `audience` now inject correctly.
+- Add regression test `tests/unit/test-jsonld-webpage.php`: exercises `retype_to_medical_webpage()` with array input for peptide and non-peptide contexts (no TypeError), and `enrich_webpage_piece` with `@type` as array (enrichment injects). Tests fail against v0.6.0, pass after fix.
+
 ## [0.6.0] — 2026-06-13
 
 ### Added