feat(10.1-02): mount plugin widget elements and run their actions from the form

- pluginAssets loads controller scripts and stylesheets from {base}/assets/ only, once per URL
- WidgetField mounts the custom element with attributes only and posts summer-action through the typed client
- Only declared fill keys returned by the server are patched; the form turns dirty and nothing saves
- widget is a registered valueless type rendered on create and update, labelled as a group
- backend::lang.extension strings in en and pl; embedded dist rebuilt

admin/src/api/types.ts

@@ -34,6 +34,12 @@ export type FilterOption = Schemas['cabana.FilterOption']
 export type RecordMeta = Schemas['cabana.RecordMeta']
 export type RecordEnvelope = Schemas['cabana.RecordEnvelope']
 export type BulkResult = Schemas['cabana.BulkResult']
+/** Body of a widget action: the record id (absent on create) and fill values. */
+export type AdminActionRequest = Schemas['cabana.AdminActionRequest']
+/** A widget or toolbar action result: the toast message and fill values. */
+export type AdminActionResult = Schemas['cabana.AdminActionResult']
+/** A controller's plugin script and stylesheet URLs under {base}/assets/. */
+export type ControllerAssets = Schemas['cabana.ControllerAssets']
 /** One message as CLDR plural forms; "other" is always present (D-13). */
 export type MessageForms = Schemas['cabana.MessageForms']
 /** The public backend::lang bundle: full key to CLDR forms (D-20). */