feat: PRAB article JSON-LD emitter + meta reader (v0.8.0)

- PR_Core_Jsonld_Article: meta-triggered emitter for PRAutoBlogger posts
  (trigger: _prab_schema_version=1 on post type). Yoast path retypes page
  node to MedicalWebPage (wpseo_schema_webpage_type priority 10) and enriches
  Article piece with citation[], about[]→Drug @id, lastReviewed, honest
  reviewedBy (wpseo_schema_graph priority 13). No-Yoast fallback emits
  standalone @graph. Posts without trigger meta are byte-unchanged.

- PR_Core_Prab_Meta_Reader: sanitises all _prab_* contract-v1 meta at read
  time. URLs validated (http/https), DOIs normalised to https://doi.org/ URI,
  JSON arrays per-element validated, WP user ID resolved. Malformed values
  degrade gracefully. Honest reviewedBy: Person ONLY when mode=human + valid
  user ID; else Organization. Never a fabricated person.

- Unit tests: JsonldArticleTest.php — 22 assertions covering is_triggered,
  review_mode, reviewed_by Person/Org decision tree, citation sanitization,
  DOI normalisation, about linkage, retype passthrough, enrich, no-new-nodes,
  editorial-system-never-person.

- bootstrap.php: WP_User stub + get_userdata reads pr_test_userdata global.
- ARCHITECTURE.md: updated JSON-LD class tree + PRAB emission section.
- CONVENTIONS.md: PRAB contract v2 extension guide added.
- CHANGELOG.md + version bump to v0.8.0.

Ratified contract: convo/prcore/decisions/2026-06-11-jsonld-contract-v1.md
File sizes: article.php=235L, meta-reader.php=265L (both < 300-line gate).
No duplicate Article/WebPage nodes. uninstall.php unaffected (_prab_* unowned).

Agent-Session: prcore-jsonld-article-20260622

includes/class-pr-core.php

@@ -19,7 +19,7 @@ declare(strict_types=1);
  * What: Registers all hooks, runs migrations, boots subsystems.
  * Who calls it: peptide-repo-core.php on plugins_loaded.
  * Dependencies: PR_Core_Migration_Runner, PR_Core_Peptide_CPT, PR_Core_Topic_Taxonomy,
- *              PR_Core_Admin, PR_Core_Disclaimer, PR_Core_Jsonld,
+ *              PR_Core_Admin, PR_Core_Disclaimer, PR_Core_Jsonld, PR_Core_Jsonld_Article,
  *              PR_Core_Rest_Controller, PR_Core_Related_Posts_Section.
  *
  * @see peptide-repo-core.php — Bootstrap that instantiates this class.
@@ -91,6 +91,9 @@ class PR_Core {
 		$jsonld = new PR_Core_Jsonld();
 		$jsonld->register_hooks();
 
+		$jsonld_article = new PR_Core_Jsonld_Article();
+		$jsonld_article->register_hooks();
+
 		// Related Articles section (frontend).
 		$related_posts = new PR_Core_Related_Posts_Section(
 			new PR_Core_Internal_Posts_Provider()