feat(2meet-data-optimizer): repair drifted flat rows from native with drift-check --fix

- TMDO_Drift_Check::fix() deletes flat rows of deleted entities and, for post groups, of posts outside the group's post types; rebuilds every other drifted entity's row from native through the new TMDO_Entity_Migration_Engine::migrate_entity() (keys without native rows become NULL, PR-066); keeps a row whose entity has no native value for the group but clears its columns (no NULL-only inserts, no deleted rows the router may join on); invalidates the row cache of each touched entity; then checks again. Native meta is never written.
- `wp tmdo drift-check <entity> --fix` (not combinable with --sample).
- Verify: DriftCheckTest fix cases (RED: method missing); dev36 --fix: post 42 rows rebuilt, 1 stray row (post 312, hp_booking in hp_draft_flags) deleted, all four entities 0 drift after, checker miss/extra 0.
- PR: PR-071

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

@@ -182,6 +182,28 @@ final class TMDO_Entity_Migration_Engine {
 		return $stats;
 	}
 
+	/**
+	 * Rebuild one entity's row of a group from native meta.
+	 *
+	 * @return bool False when native holds none of the group's keys (nothing written).
+	 */
+	public static function migrate_entity( string $entity_type, string $group_name, int $entity_id ): bool {
+		$adapter      = TMDO_Entity_Registry::get_adapter( $entity_type );
+		$group_fields = TMDO_Entity_Registry::get_group_fields( $entity_type, $group_name );
+		if ( ! $adapter || empty( $group_fields ) ) {
+			return false;
+		}
+		return self::migrate_single_entity(
+			$entity_type,
+			$group_name,
+			$entity_id,
+			array_column( $group_fields, 'key' ),
+			array_column( $group_fields, null, 'key' ),
+			$adapter,
+			false
+		);
+	}
+
 	/**
 	 * 遷移單一 entity 的所有 meta
 	 */