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/views/FormView.vue

@@ -1,15 +1,17 @@
 <script setup lang="ts">
-import { computed, nextTick, onBeforeUnmount, onMounted, ref, watchEffect } from 'vue'
+import { computed, nextTick, onBeforeUnmount, onMounted, provide, ref, watchEffect } from 'vue'
 import { onBeforeRouteLeave, onBeforeRouteUpdate, useRoute, useRouter } from 'vue-router'
 import { ArrowLeft, Trash2 } from '@lucide/vue'
 import { api } from '../api/client'
 import type { AdminRecord, ErrorEnvelope, FormView, RecordEnvelope, RecordMeta } from '../api/types'
 import { controllerIdFromParams, controllerPath } from '../app/controllerRoutes'
-import { message, t } from '../app/i18n'
+import { currentLocale, message, t } from '../app/i18n'
+import { loadControllerAssets } from '../app/pluginAssets'
 import { mapWinterUrl } from '../app/winterUrl'
 import FormErrorBanner from '../components/form/FormErrorBanner.vue'
 import FormGrid from '../components/form/FormGrid.vue'
 import FormTabs from '../components/form/FormTabs.vue'
+import { FORM_ASSETS, FORM_LOCALE, FORM_PATCH, FORM_VALUES } from '../components/form/formContext'
 import { needsRecord } from '../components/form/registry'
 import {
   DEFAULT_TAB,
@@ -63,6 +65,8 @@ const confirm = useConfirm()
 // Set right before a navigation the form itself starts after a save or a
 // delete, so the dirty guard does not ask.
 let leaving = false
+// The controller's plugin scripts: settled when every one loaded or failed.
+let assetsReady: Promise<string[]> = Promise.resolve([])
 
 // A relation manager needs a saved record: on create it is dropped with its
 // tab even when the YAML forgets `context: update` (D-05, design screen 5).
@@ -150,6 +154,10 @@ async function load(): Promise<void> {
   ])
   schema.value = schemaResult.data?.data ?? null
   failed.value = !schemaResult.data || (recordResult !== null && !recordResult.data)
+  if (schema.value) {
+    // Plugin files load in the background; only widgets wait for them (D-14).
+    assetsReady = loadControllerAssets(controllerId, schema.value.assets)
+  }
   if (schema.value && mode === 'create') {
     values.value = initialValues(fields.value)
   }
@@ -167,6 +175,14 @@ function update(name: string, value: unknown): void {
   }
 }
 
+// Extension controls (widgets) read the values and locale and write action
+// results back through update, so a fill marks the form dirty and clears
+// that field's errors like an edit (D-07, D-08).
+provide(FORM_VALUES, computed(() => values.value))
+provide(FORM_PATCH, update)
+provide(FORM_LOCALE, computed(() => schema.value?.meta.locale || currentLocale.value))
+provide(FORM_ASSETS, () => assetsReady)
+
 /** 422: messages under fields, the first invalid field (schema order) focused. */
 async function showErrors(error: ErrorEnvelope['error'] | undefined): Promise<void> {
   errors.value = fieldErrors(error?.details)