Real-Time Worker-Employer Chat System

I need a standalone chat module that plugs into my existing Worker Online platform so employers and workers can talk instantly without ever leaving the site. The core requirement is true real-time messaging—no page refreshes, no polling delays—so WebSocket technology such as Socket.IO, Pusher, Firebase Realtime DB, or a similarly reliable solution is essential.

Key capabilities I must see in the finished module
• One-to-one conversations that appear instantly on both sides
• Secure file sharing inside the chat window (PDF, DOC, image and video attachments up to a configurable size limit)
• Typing indicators, online/offline status and message timestamps
• Scalable architecture that keeps messages synced across web and mobile views
• Clean, responsive UI that inherits my current colour palette and fonts

Technical expectations
– Any modern back-end stack is fine as long as it supports WebSockets and can be containerised for deployment.
– Front-end should slot into a React environment; if you prefer another framework, show me how you will keep styling consistent.
– Code must be well organised and documented enough for my in-house dev to extend later.
– Privacy and security are a must: encrypted traffic (TLS) and server-side file validation.

Acceptance criteria
1. Two demo accounts can exchange text and files in real time with no noticeable lag (<300 ms).
2. Refreshing the browser shows the full chat history retrieved from the database.
3. Uploaded files download correctly and are stored in an access-controlled folder or object bucket.
4. A short README explains setup, environment variables and build commands.

Hand over a Git repo, a brief deployment guide, and a staging URL so I can click around before sign-off.