feat(14.2.1-06): persist nested ML maps on relation-child create

RelationService looks up TranslationWriter like CRUDService so CreateChild can lift locale maps before fillChild, write Polish after the child PK, and return a hydrated title map.

Co-authored-by: Cursor <cursoragent@cursor.com>

modules/cabana/relation.go

@@ -186,9 +186,11 @@ type RelationService struct {
 	SessionKey string
 
 	// bucket deletes the blobs of child files a save removes, after commit;
-	// tr localizes date bound messages. Both may be nil.
+	// tr localizes date bound messages. Both may be nil. writer is the same
+	// optional plugin adapter CRUDService uses for mltext/mlmarkdown.
 	bucket *blob.Bucket
 	tr     *phrasebook.Translator
+	writer TranslationWriter
 }
 
 func (s RelationSchema) MarshalJSON() ([]byte, error) {