feat: initial peptide-repo-core plugin (v0.1.0) — canonical schema sprint

Implements ADR-0002: canonical peptide schema as shared data layer for
the peptiderepo.com ecosystem. All Tier 1 tools (Reconstitution Calculator,
Dosage Reference, Legal Status Tracker, PSA enhancements) build on this.

Includes:
- pr_peptide CPT with REST, taxonomies, 11 meta fields
- 3 custom tables: pr_dosing_rows, pr_legal_cells, pr_ai_candidate_queue
- Sequential migration runner with schema versioning
- 4 typed DTOs and 4 repository classes (full CRUD)
- REST API (pr-core/v1): 6 endpoints (read public, write auth-gated)
- Admin UI: 3 meta boxes, custom columns, AI candidate queue page
- Shared disclaimer component (shortcode + static API)
- JSON-LD Drug schema emission on single peptide pages
- Seed data fixture (3 peptides, 10 dosing rows, 5 legal cells)
- Full teardown in uninstall.php
- CI: PHP lint 8.0-8.2, PHPCS WordPress, 300-line check

All 22 PHP files under 300 lines. Highest: peptide-cpt at 265.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/css/admin.css

@@ -0,0 +1,22 @@
+/**
+ * Peptide Repo Core — Admin styles.
+ * Minimal styling for meta boxes and candidate queue page.
+ */
+
+.pr-core-meta-table input.regular-text {
+	width: 100%;
+	max-width: 400px;
+}
+
+.pr-core-meta-table select {
+	min-width: 200px;
+}
+
+.pr-core-disclaimer {
+	background: #fef3cd;
+	border-left: 4px solid #ffc107;
+	padding: 12px 16px;
+	margin: 16px 0;
+	font-size: 13px;
+	line-height: 1.5;
+}