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

modules/boardwalk/dist/index.html

@@ -6,8 +6,8 @@
     <meta name="robots" content="noindex, nofollow" />
     <meta name="summer-admin-base" content="__SUMMER_ADMIN_BASE__" />
     <title>SummerCMS</title>
-    <script type="module" crossorigin src="./assets/index-BAlwlQ8W.js"></script>
-    <link rel="stylesheet" crossorigin href="./assets/index-CLf0gZ3D.css">
+    <script type="module" crossorigin src="./assets/index-CnkxaoJL.js"></script>
+    <link rel="stylesheet" crossorigin href="./assets/index-DQRkkGSM.css">
   </head>
   <body>
     <div id="app"></div>