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/ml_smoke_test.go

@@ -80,11 +80,11 @@ func (w *recordingWriter) EnabledLocales(context.Context, *gorm.DB) ([]string, e
 }
 
 func (w *recordingWriter) WriteTranslated(_ context.Context, _ *gorm.DB, model any, field, locale, value string) error {
-	post, _ := model.(*mlPost)
-	if post == nil || post.ID == 0 {
+	id := pkUint(model)
+	if id == 0 {
 		return &ValidationError{Details: map[string]any{field: []string{"translation writer ran before the host row had an id"}}}
 	}
-	w.ids = append(w.ids, post.ID)
+	w.ids = append(w.ids, id)
 	if w.attrs == nil {
 		w.attrs = map[string]map[string]string{}
 	}