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/field_ml.go

@@ -10,6 +10,7 @@ import (
 
 const (
 	mlTextFieldType     = "mltext"
+	mlTextareaFieldType = "mltextarea"
 	mlMarkdownFieldType = "mlmarkdown"
 )
 
@@ -41,11 +42,17 @@ type mlValue struct {
 	values map[string]string
 }
 
+// mlFieldType reports whether typ is a multilingual field type whose value is
+// a locale map: mltext, mltextarea or mlmarkdown.
 func mlFieldType(typ string) bool {
-	return typ == mlTextFieldType || typ == mlMarkdownFieldType
+	switch typ {
+	case mlTextFieldType, mlTextareaFieldType, mlMarkdownFieldType:
+		return true
+	}
+	return false
 }
 
-// liftMLValues takes declared mltext/mlmarkdown maps out of a save body
+// liftMLValues takes declared mltext/mltextarea/mlmarkdown maps out of a save body
 // before ProjectWritableFields drops nested values. Only fields present in
 // the body whose context allows op are lifted. A value must be a JSON object
 // of enabled locale code to string; unknown locales, extra keys, and
@@ -167,8 +174,8 @@ func applyMLTranslations(ctx context.Context, tx *gorm.DB, writer TranslationWri
 	return nil
 }
 
-// hydrateMLRecord replaces host scalars of declared mltext/mlmarkdown fields
-// in a Show/save RecordResult.Data map with a locale→text map for every
+// hydrateMLRecord replaces host scalars of declared mltext/mltextarea/mlmarkdown
+// fields in a Show/save RecordResult.Data map with a locale→text map for every
 // enabled code. The default locale is the projected host column; other codes
 // come from TranslatedExact; a missing non-default code is an empty string,
 // never D-11 fallback. It is a no-op when writer is nil and is not used from