feat(2meet-data-optimizer-hivepress-addon): provide HivePress defaults to core via filters

- TMDO_HivePress_Entity_Groups hooks tmdo_rest_default_post_type so GET /wpdo/v1/listings keeps defaulting to hp_listing now that core defaults to 'post' (PR-020e)
- Test: TMDO_Post_Group_Reconciler::plan() over the AddOn's groups yields the 8 misrouted HivePress keys (coverage moved out of core in PR-020b)
- Verify: HP unit 148 / integration 49 OK, bootstrap smoke OK
- PR: PR-020f

includes/class-tmdo-hivepress-entity-groups.php

@@ -32,12 +32,22 @@ if ( ! defined( 'ABSPATH' ) ) {
 final class TMDO_HivePress_Entity_Groups {
 
 	/**
-	 * Hook into WPDO entity field registration.
+	 * Hook into WPDO entity field registration and the REST default post type.
 	 *
 	 * @return void
 	 */
 	public static function register(): void {
 		add_action( 'wpdo_register_entity_fields', array( __CLASS__, 'register_entity_fields' ) );
+		add_filter( 'tmdo_rest_default_post_type', array( __CLASS__, 'rest_default_post_type' ) );
+	}
+
+	/**
+	 * GET /wpdo/v1/listings serves HivePress listings when no post type is given.
+	 *
+	 * @return string
+	 */
+	public static function rest_default_post_type(): string {
+		return 'hp_listing';
 	}
 
 	/**