feat: add batch processing for multiple file uploads

- Add BatchState management in taskStore with progress tracking
- Implement batch processing service with concurrency control
  - Direct Track: max 5 parallel tasks
  - OCR Track: sequential processing (GPU VRAM limit)
- Refactor ProcessingPage to support batch mode with BatchProcessingPanel
- Update UploadPage to initialize batch state for multi-file uploads
- Add i18n translations for batch processing (zh-TW, en-US)

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

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

frontend/src/pages/ProcessingPage.tsx

@@ -14,11 +14,30 @@ import PreprocessingSettings from '@/components/PreprocessingSettings'
 import PreprocessingPreview from '@/components/PreprocessingPreview'
 import ProcessingTrackSelector from '@/components/ProcessingTrackSelector'
 import TaskNotFound from '@/components/TaskNotFound'
+import BatchProcessingPanel from '@/components/BatchProcessingPanel'
 import { useTaskValidation } from '@/hooks/useTaskValidation'
-import { useTaskStore, useProcessingState } from '@/store/taskStore'
+import { useTaskStore, useProcessingState, useIsBatchMode } from '@/store/taskStore'
 import type { LayoutModel, ProcessingOptions, PreprocessingMode, PreprocessingConfig, ProcessingTrack } from '@/types/apiV2'
 
+/**
+ * ProcessingPage - Main entry point
+ * Routes to batch or single task processing based on state
+ */
 export default function ProcessingPage() {
+  const isBatchMode = useIsBatchMode()
+
+  // Route to appropriate component
+  if (isBatchMode) {
+    return <BatchProcessingPanel />
+  }
+
+  return <SingleTaskProcessing />
+}
+
+/**
+ * SingleTaskProcessing - Original single task processing UI
+ */
+function SingleTaskProcessing() {
   const { t } = useTranslation()
   const navigate = useNavigate()
   const { toast } = useToast()