fix: resume translation polling when returning to task detail page

Add useEffect to check for in-progress translations on page load.
This ensures that if user navigates away during translation and
returns, the UI will resume polling and show completion status.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/TaskDetailPage.tsx

@@ -107,6 +107,32 @@ export default function TaskDetailPage() {
     retry: false,
   })
 
+  // Check for in-progress translation on page load
+  useEffect(() => {
+    if (!taskId || !taskDetail || taskDetail.status !== 'completed') return
+
+    const checkTranslationStatus = async () => {
+      try {
+        const status = await apiClientV2.getTranslationStatus(taskId)
+        if (status.status === 'translating' || status.status === 'pending') {
+          // Resume polling for in-progress translation
+          setIsTranslating(true)
+          setTranslationStatus(status.status)
+          if (status.progress) {
+            setTranslationProgress(status.progress.percentage)
+          }
+          if (status.target_lang) {
+            setTargetLang(status.target_lang)
+          }
+        }
+      } catch {
+        // No active translation job - this is normal
+      }
+    }
+
+    checkTranslationStatus()
+  }, [taskId, taskDetail])
+
   // Poll translation status when translating
   useEffect(() => {
     if (!isTranslating || !taskId) return