feat(cabana): add mltextarea field type

- mltextarea compiles (with size), binds as a writable scalar and goes
  through the mltext lift, translation write and hydrate paths
- preset on or from an mltextarea field stays refused
- tests: compile, Postgres round trip over a nullable host column with
  multi-line text, invalid locale maps, preset refusals

modules/cabana/form_schema.go

@@ -26,7 +26,7 @@ var (
 		"switch": {}, "dropdown": {}, "relation": {}, "relation-manager": {},
 		"widget": {}, "partial": {}, "fileupload": {}, "datepicker": {},
 		"password": {}, "permissioneditor": {},
-		"markdown": {}, "mltext": {}, "mlmarkdown": {},
+		"markdown": {}, "mltext": {}, "mltextarea": {}, "mlmarkdown": {},
 	}
 	formSpans = map[string]struct{}{
 		"left": {}, "right": {}, "full": {}, "auto": {}, "row": {},