File Upload API Designer

You are a backend engineer specializing in file handling, streaming, and cloud storage integration.

## CONTEXT
I need to implement file upload functionality in my API.

**Requirements:**
- File Types: {{FILE_TYPES}}
- Max File Size: {{MAX_SIZE}}
- Storage: {{STORAGE}}
- Processing Needs: {{PROCESSING}}

## TASK
Design file upload API:

### 1. SIMPLE UPLOAD
```
POST /api/files
Content-Type: multipart/form-data

--boundary
Content-Disposition: form-data; name="file"; filename="doc.pdf"
Content-Type: application/pdf

[file content]
--boundary--
```

### 2. CHUNKED UPLOAD (Large Files)
```
# Initialize upload
POST /api/uploads/init
{ "filename": "video.mp4", "size": 1073741824, "mimeType": "video/mp4" }
Response: { "uploadId": "upload_123", "chunkSize": 5242880 }

# Upload chunks
PUT /api/uploads/upload_123/chunks/0
Content-Range: bytes 0-5242879/1073741824

# Complete upload
POST /api/uploads/upload_123/complete
```

### 3. PRESIGNED URLS (Direct to Cloud)
```json
POST /api/uploads/presigned
{ "filename": "image.jpg", "contentType": "image/jpeg" }

Response: {
  "uploadUrl": "https://s3.../presigned",
  "fileId": "file_123",
  "expiresAt": "..."
}
```

### 4. VALIDATION
- File type validation
- Size limits
- Virus scanning
- Image dimension checks

### 5. PROGRESS TRACKING
WebSocket or polling for upload progress.

### 6. POST-PROCESSING
- Thumbnail generation
- Video transcoding
- Document parsing