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/relation.go

@@ -187,7 +187,7 @@ type RelationService struct {
 
 	// bucket deletes the blobs of child files a save removes, after commit;
 	// tr localizes date bound messages. Both may be nil. writer is the same
-	// optional plugin adapter CRUDService uses for mltext/mlmarkdown.
+	// optional plugin adapter CRUDService uses for mltext/mltextarea/mlmarkdown.
 	bucket *blob.Bucket
 	tr     *phrasebook.Translator
 	writer TranslationWriter