Implement file upload with Redis pub/sub progress tracking

[VrindaBansal]

Summary

This PR implements file upload functionality with real-time progress tracking through Redis pub/sub, integrating with the expandable WebSocket architecture.

Changes

• Redis pub/sub integration: Added Redis client for publishing progress updates
• publishProgress() helper: Reusable function for publishing to any Redis channel
• Real-time progress tracking: Progress updates published to "file-upload" channel
• Chunked processing simulation: 10 chunks with individual progress updates (0-100%)
• Error handling: Failed status published on errors with error messages
• File upload support: Multer configuration with 10MB limit and memory storage

How It Works

1. Client uploads file via POST /api/file-upload
2. Server generates unique jobId and returns 202 response
3. Progress updates published to Redis "file-upload" channel
4. WebSocket server forwards updates to subscribed clients
5. Frontend displays real-time progress

Message Format

{
  jobId: string,
  status: "processing" | "completed" | "failed",
  progress: number, // 0-100
  fileName: string,
  fileSize: number,
  message?: string,
  timestamp: number
}

Integration

Works seamlessly with:

• Bitrix-Websocket-Server (subscribes to "file-upload" channel)
• Bitrix24 frontend (useWebSocket hook with channel filtering)

Template for New Job Types

This implementation serves as a template. Copy the publishProgress() pattern to add new job types by publishing to different channels.