feat: implement hybrid image extraction and memory management

Backend:
- Add hybrid image extraction for Direct track (inline image blocks)
- Add render_inline_image_regions() fallback when OCR doesn't find images
- Add check_document_for_missing_images() for detecting missing images
- Add memory management system (MemoryGuard, ModelManager, ServicePool)
- Update pdf_generator_service to handle HYBRID processing track
- Add ElementType.LOGO for logo extraction

Frontend:
- Fix PDF viewer re-rendering issues with memoization
- Add TaskNotFound component and useTaskValidation hook
- Disable StrictMode due to react-pdf incompatibility
- Fix task detail and results page loading states

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

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

frontend/src/hooks/useTaskValidation.ts

@@ -0,0 +1,64 @@
+import { useEffect, useState } from 'react'
+import { useQuery } from '@tanstack/react-query'
+import { useUploadStore } from '@/store/uploadStore'
+import { apiClientV2 } from '@/services/apiV2'
+import type { TaskDetail } from '@/types/apiV2'
+
+interface UseTaskValidationResult {
+  taskId: string | null
+  taskDetail: TaskDetail | undefined
+  isLoading: boolean
+  isNotFound: boolean
+  clearAndReset: () => void
+}
+
+/**
+ * Hook for validating task existence and handling deleted tasks gracefully.
+ * Shows loading state first, then either returns task data or marks as not found.
+ */
+export function useTaskValidation(options?: {
+  refetchInterval?: number | false | ((query: any) => number | false)
+}): UseTaskValidationResult {
+  const { batchId, clearUpload } = useUploadStore()
+  const taskId = batchId ? String(batchId) : null
+
+  const [isNotFound, setIsNotFound] = useState(false)
+
+  const { data: taskDetail, isLoading, error, isFetching } = useQuery({
+    queryKey: ['taskDetail', taskId],
+    queryFn: () => apiClientV2.getTask(taskId!),
+    enabled: !!taskId && !isNotFound,
+    retry: (failureCount, error: any) => {
+      // Don't retry on 404
+      if (error?.response?.status === 404) {
+        return false
+      }
+      return failureCount < 2
+    },
+    refetchInterval: options?.refetchInterval ?? false,
+    // Disable stale time to ensure we check fresh data
+    staleTime: 0,
+  })
+
+  // Handle 404 error - mark as not found immediately
+  useEffect(() => {
+    if (error && (error as any)?.response?.status === 404) {
+      setIsNotFound(true)
+    }
+  }, [error])
+
+  // Clear state and store
+  const clearAndReset = () => {
+    clearUpload()
+    setIsNotFound(false)
+  }
+
+  return {
+    taskId,
+    taskDetail,
+    // Show loading if we have a taskId and are still fetching (but not if already marked as not found)
+    isLoading: !!taskId && !isNotFound && (isLoading || isFetching) && !taskDetail,
+    isNotFound,
+    clearAndReset,
+  }
+}