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>

includes/dto/class-pr-core-legal-cell-dto.php

@@ -0,0 +1,75 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Typed data-transfer object for a legal status cell.
+ *
+ * What: Immutable value object wrapping a row from pr_legal_cells.
+ * Who calls it: PR_Core_Legal_Repository returns these; consumers read them.
+ * Dependencies: None.
+ *
+ * @see migrations/class-pr-core-migration-0002-legal-cells.php — Table schema.
+ * @see repositories/class-pr-core-legal-repository.php         — Creates these from DB rows.
+ */
+class PR_Core_Legal_Cell_DTO {
+
+	public readonly int $id;
+	public readonly int $peptide_id;
+	public readonly string $country_code;
+	public readonly string $status;
+	public readonly ?string $regulatory_framework;
+	public readonly ?string $regulatory_text_url;
+	public readonly ?string $regulatory_text_quote;
+	public readonly ?string $notes;
+	public readonly string $last_verified_at;
+	public readonly int $schema_version;
+	public readonly int $reviewer_id;
+	public readonly ?int $superseded_by_id;
+
+	/**
+	 * @param array<string, mixed> $data Associative array from database row.
+	 */
+	public function __construct( array $data ) {
+		$this->id                    = (int) ( $data['id'] ?? 0 );
+		$this->peptide_id            = (int) ( $data['peptide_id'] ?? 0 );
+		$this->country_code          = (string) ( $data['country_code'] ?? '' );
+		$this->status                = (string) ( $data['status'] ?? 'unclear' );
+		$this->regulatory_framework  = $data['regulatory_framework'] ?? null;
+		$this->regulatory_text_url   = $data['regulatory_text_url'] ?? null;
+		$this->regulatory_text_quote = $data['regulatory_text_quote'] ?? null;
+		$this->notes                 = $data['notes'] ?? null;
+		$this->last_verified_at      = (string) ( $data['last_verified_at'] ?? '' );
+		$this->schema_version        = (int) ( $data['schema_version'] ?? 1 );
+		$this->reviewer_id           = (int) ( $data['reviewer_id'] ?? 0 );
+		$this->superseded_by_id      = isset( $data['superseded_by_id'] ) ? (int) $data['superseded_by_id'] : null;
+	}
+
+	/**
+	 * Check if this cell is the active (non-superseded) version.
+	 *
+	 * @return bool
+	 */
+	public function is_active(): bool {
+		return null === $this->superseded_by_id;
+	}
+
+	/**
+	 * Convert to associative array for REST/admin output.
+	 *
+	 * @return array<string, mixed>
+	 */
+	public function to_array(): array {
+		return [
+			'id'                    => $this->id,
+			'peptide_id'            => $this->peptide_id,
+			'country_code'          => $this->country_code,
+			'status'                => $this->status,
+			'regulatory_framework'  => $this->regulatory_framework,
+			'regulatory_text_url'   => $this->regulatory_text_url,
+			'regulatory_text_quote' => $this->regulatory_text_quote,
+			'notes'                 => $this->notes,
+			'last_verified_at'      => $this->last_verified_at,
+			'is_active'             => $this->is_active(),
+		];
+	}
+}