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/class-pr-core-autoloader.php

@@ -0,0 +1,64 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * SPL autoloader for PR_Core_ prefixed classes.
+ *
+ * What: Resolves PR_Core_ class names to file paths under includes/.
+ * Who calls it: peptide-repo-core.php bootstrap.
+ * Dependencies: None.
+ *
+ * Naming convention: PR_Core_Foo_Bar => class-pr-core-foo-bar.php.
+ * Scans includes/ and all immediate subdirectories.
+ *
+ * @see peptide-repo-core.php — Registers this autoloader at boot.
+ */
+class PR_Core_Autoloader {
+
+	/** @var string[] Directories to scan for class files. */
+	private static array $dirs = [];
+
+	/**
+	 * Register the autoloader with SPL.
+	 *
+	 * Side effects: calls spl_autoload_register().
+	 *
+	 * @return void
+	 */
+	public static function register(): void {
+		$base = PR_CORE_PLUGIN_DIR . 'includes/';
+
+		self::$dirs[] = $base;
+
+		// Add all immediate subdirectories.
+		foreach ( glob( $base . '*', GLOB_ONLYDIR ) as $dir ) {
+			self::$dirs[] = trailingslashit( $dir );
+		}
+
+		spl_autoload_register( [ __CLASS__, 'load' ] );
+	}
+
+	/**
+	 * Autoload callback. Only handles PR_Core_ prefixed classes.
+	 *
+	 * @param string $class Fully-qualified class name.
+	 * @return void
+	 */
+	public static function load( string $class ): void {
+		if ( 0 !== strpos( $class, 'PR_Core_' ) ) {
+			return;
+		}
+
+		// PR_Core_Foo_Bar => foo-bar => class-pr-core-foo-bar.php.
+		$suffix   = substr( $class, 8 ); // Strip 'PR_Core_'.
+		$filename = 'class-pr-core-' . str_replace( '_', '-', strtolower( $suffix ) ) . '.php';
+
+		foreach ( self::$dirs as $dir ) {
+			$path = $dir . $filename;
+			if ( file_exists( $path ) ) {
+				require_once $path;
+				return;
+			}
+		}
+	}
+}