feat: verification scanner + admin UI (PR Core v0.4.0)

Implements recurring verification scanner, dashboard widget, per-post sidebar meta box, reader-facing last-verified display, and unified settings panel. Bumps to v0.4.0.

Co-authored-by: peptiderepo <peptiderepo@users.noreply.github.com>

includes/cpt/class-pr-core-verification-sanitizers.php

@@ -0,0 +1,34 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Sanitizers for verification meta fields.
+ *
+ * What: Standalone sanitization functions for verification_velocity and verification_status fields.
+ * Who calls it: PR_Core_Peptide_CPT::get_meta_fields() sanitize callbacks.
+ * Dependencies: None.
+ *
+ * @see cpt/class-pr-core-peptide-cpt.php — Calls these from meta field registration.
+ */
+class PR_Core_Verification_Sanitizers {
+
+	/**
+	 * Sanitize verification_velocity to allowed enum values.
+	 *
+	 * @param string $value Raw input.
+	 * @return string Valid enum value (low, medium, high).
+	 */
+	public static function sanitize_velocity( string $value ): string {
+		return in_array( $value, [ 'low', 'medium', 'high' ], true ) ? $value : 'medium';
+	}
+
+	/**
+	 * Sanitize verification_status to allowed enum values.
+	 *
+	 * @param string $value Raw input.
+	 * @return string Valid enum value (current, due, overdue).
+	 */
+	public static function sanitize_status( string $value ): string {
+		return in_array( $value, [ 'current', 'due', 'overdue' ], true ) ? $value : 'current';
+	}
+}