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/class-pr-core-deactivator.php

@@ -21,6 +21,10 @@ class PR_Core_Deactivator {
 	 * @return void
 	 */
 	public static function deactivate(): void {
+		// Clear verification scan cron.
+		wp_clear_scheduled_hook( 'pr_core_verification_scan' );
+
+		// Flush rewrite rules.
 		flush_rewrite_rules();
 	}
 }