feat(12.1-02): read-only preview screen with a status hint and record actions

- config_form.yaml preview block (optional headerPartial), reported in the form schema as preview
- fields with context: preview show only on the preview screen and are never written
- form messages preview and edit; recordActions without a preview block stops boot
- SPA route {id}/preview, PreviewView and PreviewField, record actions in the footer
- mapWinterUrl maps preview/:id; the update form returns to the preview
- summer-callout partial style classes for status hints
- README, docs, OpenAPI document, TS types and the embedded build updated

admin/src/views/FormView.vue

@@ -51,7 +51,7 @@ const path = {
 }
 const controllerId = controllerIdFromParams(path)
 const listPath = controllerPath(controllerId) ?? '/'
-const mode: FormMode = route.name === 'create' ? 'create' : 'update'
+const mode: Exclude<FormMode, 'preview'> = route.name === 'create' ? 'create' : 'update'
 const recordId = mode === 'update' ? Number(route.params.id) : null
 
 const schema = ref<FormView | null>(null)
@@ -152,6 +152,11 @@ const subtitle = computed(() =>
   mode === 'update' ? message(schema.value?.messages.update, undefined, { name: recordName.value }) : '',
 )
 
+// An update form of a record that has a preview screen is entered from it,
+// so back and Cancel return there (UI-SPEC S3); a delete still goes to the list.
+const backToPreview = computed(() => mode === 'update' && !!schema.value?.preview)
+const backPath = computed(() => (backToPreview.value ? `${listPath}/${recordId}/preview` : listPath))
+
 const dirty = computed(
   () =>
     !loading.value &&
@@ -366,7 +371,7 @@ async function onLeave(): Promise<void> {
       return
     }
   }
-  await go(listPath)
+  await go(backPath.value)
 }
 
 onBeforeRouteLeave(guard)
@@ -395,7 +400,7 @@ void load()
       <Button
         variant="outline"
         data-action="back"
-        :aria-label="t('backend::lang.form.return_to_list')"
+        :aria-label="t(backToPreview ? 'backend::lang.form.return_to_preview' : 'backend::lang.form.return_to_list')"
         class="size-10! px-0!"
         @click="onLeave"
       >