fix(2meet-data-optimizer): entity health sees a running backfill

- Backfill batches are scheduled with (entity, group) args; the health
  panel looked for (entity) alone, never saw one and kept offering to start
  a backfill, which resets the group's checkpoint
- is_backfill_active() checks every group of the entity
- Unit bootstrap: wp_next_scheduled() stub honours hook + args
- Verify: EntityHealthBackfillTest (2 new); unit 711, phpcs 0, stan OK
- PR: PR-137 (manual F-11)

includes/engine/class-tmdo-entity-health.php

@@ -325,7 +325,20 @@ final class TMDO_Entity_Health {
 		return TMDO_Mode_Manager::ALL_MODES[ $idx - 1 ];
 	}
 
+	/**
+	 * Whether a backfill batch is scheduled for any group of the entity. Batches
+	 * are scheduled with (entity, group) args, so looking for (entity) alone
+	 * never found one (2.4.2 PR-137).
+	 *
+	 * @param string $entity_type Entity type.
+	 * @return bool
+	 */
 	private static function is_backfill_active( string $entity_type ): bool {
-		return (bool) wp_next_scheduled( 'wpdo_entity_backfill_batch', array( $entity_type ) );
+		foreach ( TMDO_Entity_Registry::get_groups_for_type( $entity_type ) as $group ) {
+			if ( wp_next_scheduled( 'wpdo_entity_backfill_batch', array( $entity_type, $group ) ) ) {
+				return true;
+			}
+		}
+		return false;
 	}
 }