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/components/form/FormField.vue

@@ -3,7 +3,7 @@ import { computed } from 'vue'
 import { CircleAlert } from '@lucide/vue'
 import type { ControllerParams, FormField, RelationOption } from '../../api/types'
 import FieldRenderer from './FieldRenderer.vue'
-import { ownsLabel } from './registry'
+import { groupLabelled, ownsLabel } from './registry'
 
 // One form row: label (600, red aria-hidden asterisk when required), the
 // control, the comment and the error line linked by aria-describedby.
@@ -25,6 +25,9 @@ const commentId = computed(() => `${base.value}-comment`)
 const errorId = computed(() => `${base.value}-error`)
 const invalid = computed(() => (props.errors?.length ?? 0) > 0)
 const selfLabelled = computed(() => ownsLabel(props.field.type))
+// A widget or partial row labels a role="group" host, so its label is a span
+// the host names with aria-labelledby, not a label for an input.
+const labelsGroup = computed(() => groupLabelled(props.field.type))
 const showComment = computed(() => !selfLabelled.value && !!props.field.comment)
 
 const describedBy = computed(() =>
@@ -36,7 +39,10 @@ const describedBy = computed(() =>
 
 <template>
   <div class="flex min-w-0 flex-col gap-1.5" :data-field="field.name">
-    <label v-if="!selfLabelled" :for="controlId" class="font-semibold">
+    <span v-if="labelsGroup" :id="`${controlId}-label`" class="font-semibold">
+      {{ field.label || field.name }}<span v-if="field.required" class="text-danger" aria-hidden="true"> *</span>
+    </span>
+    <label v-else-if="!selfLabelled" :for="controlId" class="font-semibold">
       {{ field.label || field.name }}<span v-if="field.required" class="text-danger" aria-hidden="true"> *</span>
     </label>
     <FieldRenderer