feat(admin-web): surface generation error message and speed up active polling

Hoists hasActiveGenerationStatus into the shared display helper so all
views agree on what counts as in-flight generation, shows the backend
generation_error_message inline on the imitation list and detail drawer
when status is failed, and drops the workspace/templates/imitation poll
interval from 10s to 3s (with a 5s fallback when streaming is enabled)
plus explicit query-cache invalidation so failed/completed states show
up promptly.

apps/admin-web/src/views/TemplatesView.vue

@@ -39,6 +39,7 @@ import {
   formatDateTime,
   getGenerateStatusMeta,
   getPublishStatusMeta,
+  hasActiveGenerationStatus,
   getTemplateMeta,
 } from '@/lib/display'
 import { formatError } from '@/lib/errors'
@@ -197,12 +198,6 @@ const displayedArticleTotal = computed(() =>
 
 let articlePollingTimer: number | null = null
 
-function hasActiveGenerationStatus(status?: string | null): boolean {
-  return (
-    status === 'queued' || status === 'pending' || status === 'generating' || status === 'running'
-  )
-}
-
 const deleteMutation = useMutation({
   mutationFn: (articleId: number) => articlesApi.remove(articleId),
   onSuccess: async () => {
@@ -413,8 +408,10 @@ function startArticlePolling(): void {
   }
 
   articlePollingTimer = window.setInterval(() => {
+    void queryClient.invalidateQueries({ queryKey: ['articles'] })
+    void queryClient.invalidateQueries({ queryKey: ['workspace', 'recent-articles'] })
     void Promise.all([articleListQuery.refetch(), recentArticlesQuery.refetch()])
-  }, 10000)
+  }, 3000)
 }
 
 function stopArticlePolling(): void {