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/admin_openapi.go

@@ -657,7 +657,7 @@ func AdminShow() {}
 // AdminUpdate documents the record update route.
 //
 // @Summary Update an admin record
-// @Description A plugin field type's value is decoded by its type inside the save. When a type reports what it changed, meta.notices lists the localized messages per field (and content locale), and the key is absent otherwise.
+// @Description A plugin field type's value is decoded by its type inside the save; a value equal to the one the form was served for that field and locale is neither decoded nor written. When a type reports what it changed, meta.notices lists the localized messages per field (and content locale), and the key is absent otherwise.
 // @Tags admin
 // @Accept json
 // @Produce json
@@ -1171,6 +1171,29 @@ func AdminFileList() {}
 // @Router /{vendor}/{plugin}/{controller}/{id}/files/{field} [post]
 func AdminFileUpload() {}
 
+// AdminFieldUpload documents the upload route of a plugin field type.
+//
+// @Summary Upload a file for a plugin field type
+// @Description Stores one multipart part named file through the Upload of the field's plugin field type (pact.FormFieldType) and answers its URL. id 0 is the create form and passes no record; any other id loads the record through the controller's FormExtendQuery scope. A field that is not in the form, has a built-in type, has a type without Upload or whose context does not allow the operation answers 404, as does a record outside the scope. A body over http.body_limits.upload_bytes answers 413; a malformed body, a second part or a value the type refuses (pact.FormFieldError) answers 422 on the field.
+// @Tags admin
+// @Accept multipart/form-data
+// @Produce json
+// @Security BackendBearer
+// @Param vendor path string true "Vendor"
+// @Param plugin path string true "Plugin"
+// @Param controller path string true "Controller"
+// @Param id path integer true "Record id (0 for the create form)"
+// @Param field path string true "Field name"
+// @Param file formData file true "The file"
+// @Success 201 {object} Envelope[FieldUploadResponse]
+// @Failure 401 {object} ErrorEnvelope
+// @Failure 403 {object} ErrorEnvelope
+// @Failure 404 {object} ErrorEnvelope
+// @Failure 413 {object} ErrorEnvelope
+// @Failure 422 {object} ErrorEnvelope
+// @Router /{vendor}/{plugin}/{controller}/{id}/fields/{field}/upload [post]
+func AdminFieldUpload() {}
+
 // AdminFileUpdate documents the caption route of a fileupload field.
 //
 // @Summary Save a file's title and description