Add comprehensive file management system with admin/user separation

Features added:
- Admin interface with full CRUD operations and multi-file upload
- User interface with read-only access and download functionality
- Board-style table layout with pagination (10 items per page)
- Category-specific file icons and attachment management
- Drag & drop file upload with preview and individual file removal
- Individual and bulk download with ZIP compression support
- Offline mode with localStorage fallback for both interfaces
- Responsive design with modern UI components

Technical improvements:
- Separated admin (/admin/) and user (/) interfaces
- Enhanced file data structure with consistent naming
- Improved error handling and user notifications
- Multi-file upload processing with base64 encoding
- File type detection and appropriate icon mapping
- Download functionality with single/multiple file handling

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

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

clean-storage-setup.sql

@@ -0,0 +1,62 @@
+-- 완전 초기화 후 Storage 정책 재설정
+
+-- 1단계: 모든 기존 Storage 정책 삭제
+DROP POLICY IF EXISTS "Users can upload to own folder" ON storage.objects;
+DROP POLICY IF EXISTS "Users can view own files" ON storage.objects;
+DROP POLICY IF EXISTS "Users can update own files" ON storage.objects;
+DROP POLICY IF EXISTS "Users can delete own files" ON storage.objects;
+DROP POLICY IF EXISTS "Public upload for testing" ON storage.objects;
+DROP POLICY IF EXISTS "Public read for testing" ON storage.objects;
+
+-- 혹시 다른 이름으로 생성된 정책들도 삭제
+DROP POLICY IF EXISTS "Enable insert for authenticated users only" ON storage.objects;
+DROP POLICY IF EXISTS "Enable select for authenticated users only" ON storage.objects;
+DROP POLICY IF EXISTS "Enable update for authenticated users only" ON storage.objects;
+DROP POLICY IF EXISTS "Enable delete for authenticated users only" ON storage.objects;
+
+-- 2단계: RLS 활성화 확인 (보통 이미 활성화되어 있음)
+ALTER TABLE storage.objects ENABLE ROW LEVEL SECURITY;
+
+-- 3단계: 새 정책 생성
+-- 업로드 정책
+CREATE POLICY "Users can upload to own folder"
+ON storage.objects
+FOR INSERT 
+WITH CHECK (
+    bucket_id = 'files' AND 
+    auth.uid()::text = (storage.foldername(name))[1]
+);
+
+-- 조회 정책
+CREATE POLICY "Users can view own files"
+ON storage.objects
+FOR SELECT 
+USING (
+    bucket_id = 'files' AND 
+    auth.uid()::text = (storage.foldername(name))[1]
+);
+
+-- 업데이트 정책
+CREATE POLICY "Users can update own files"
+ON storage.objects
+FOR UPDATE 
+USING (
+    bucket_id = 'files' AND 
+    auth.uid()::text = (storage.foldername(name))[1]
+);
+
+-- 삭제 정책
+CREATE POLICY "Users can delete own files"
+ON storage.objects
+FOR DELETE 
+USING (
+    bucket_id = 'files' AND 
+    auth.uid()::text = (storage.foldername(name))[1]
+);
+
+-- 4단계: 정책 생성 확인
+SELECT 
+    'Storage policies created successfully!' as message,
+    COUNT(*) as policy_count
+FROM pg_policies 
+WHERE schemaname = 'storage' AND tablename = 'objects';