feat(16.2-01): translatable plugin field types, untouched skip, writes, list values and uploads

- translatable types lift, store and hydrate through the ML path
  (isMLField); Decode and Load run per locale and notices carry the locale
- on update a value equal to the served value (Load of the stored host
  value or exact translation) is neither decoded nor written
- FieldWrite, FieldWritesFromContext and WithFieldWrites expose what a save
  writes to the Form hooks
- list columns may use a plugin alias and show the type's ListValue
- POST .../{id}/fields/{field}/upload hands the file to the type's Upload
  (guard, X-Requested-With, permissions, field context, record scope, body
  cap); OpenAPI, route inventories, README and docs updated

modules/cabana/http.go

@@ -355,6 +355,10 @@ func (s *service) mount(r pact.Router) {
 		constrainFileID(g)
 		g.Get("/{vendor}/{plugin}/{controller}/{id}/files/{field}/{file}/thumb", s.fileThumb)
 		constrainFileID(g)
+		// Uploads of plugin field type elements (D-18): cabana owns the route,
+		// the type's Upload only stores the file. {id} 0 is the create form.
+		g.Post("/{vendor}/{plugin}/{controller}/{id}/fields/{field}/upload", requireAjax(s.fieldUpload))
+		constrainFile(g)
 	})
 	// The SPA shell: public, no guard. ServeMux prefers every API pattern
 	// above over the {path...} wildcard.
@@ -1074,6 +1078,13 @@ func (s *service) operationDeclared(w http.ResponseWriter, r *http.Request, cc *
 }
 
 func projectRow(row any, controller pact.AdminController, cols []ListColumn) map[string]any {
+	return projectRowCtx(context.Background(), row, controller, cols)
+}
+
+// projectRowCtx is one list row: the id and every visible column. A column
+// whose type is a plugin field type with ListValue shows the type's text for
+// the stored value.
+func projectRowCtx(ctx context.Context, row any, controller pact.AdminController, cols []ListColumn) map[string]any {
 	v := reflect.ValueOf(row)
 	for v.Kind() == reflect.Pointer {
 		if v.IsNil() {
@@ -1100,6 +1111,10 @@ func projectRow(row any, controller pact.AdminController, cols []ListColumn) map
 		if !field.IsValid() || !field.CanInterface() {
 			continue
 		}
+		if ft := col.fieldType; ft != nil && ft.def.ListValue != nil {
+			out[col.Key] = ft.def.ListValue(ctx, derefValue(field.Interface()))
+			continue
+		}
 		out[col.Key] = field.Interface()
 	}
 	return out