fix: timeline disappears after QC re-render

- Set staleTime=0 on useAccessibleVideoEditState so edit-state is
  immediately refetched when invalidated after render completes
- Force prevJobStatusRef='rendering_qc' at render start so the
  pending_qc completion effect always fires, even when fast renders
  complete before the 10s polling interval catches rendering_qc status

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/hooks/useAccessibleVideoEdit.ts

@@ -1,4 +1,4 @@
-import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { useQuery, useMutation, useQueryClient, keepPreviousData } from '@tanstack/react-query';
 import { apiClient } from '../lib/api';
 
 /**
@@ -9,8 +9,9 @@ export function useAccessibleVideoEditState(jobId: string, language: string) {
     queryKey: ['jobs', jobId, 'accessible-video', language, 'edit-state'],
     queryFn: () => apiClient.getAccessibleVideoEditState(jobId, language),
     enabled: !!jobId && !!language,
-    staleTime: 30000, // 30 seconds
+    staleTime: 0,
     refetchOnWindowFocus: false,
+    placeholderData: keepPreviousData,
   });
 }
 

frontend/src/routes/admin/QCDetail.tsx

@@ -523,6 +523,9 @@ export function QCDetail() {
     if (!id) return;
 
     try {
+      // Force prevJobStatusRef to 'rendering_qc' so the completion effect fires
+      // even if polling misses the rendering_qc state (fast renders < 10s)
+      prevJobStatusRef.current = 'rendering_qc';
       await rerenderMutation.mutateAsync({
         jobId: id,
         language: selectedLanguage,