feat(backend): implement collaboration service

[ncduy0303]

Collaboration Service Implementation

This PR introduces a collaboration service backend that enables real-time collaborative coding sessions with persistent document storage using Y.js and MongoDB.

Data Schema

Room Model

{
  room_id: string,
  question_id: string,
  user_ids: string[],
  programmingLanguage: enum,
  isActive: boolean,
  created_at: timestamp,
  updated_at: timestamp,
  closed_at: timestamp
}

Y-doc Storage

• Each room's document stored as MongoDB collection (room_id = collection name)
• Real-time updates persisted as individual documents in the collection
• Full document reconstruction by combining all deltas

API Endpoints

REST API

Method	Endpoint	Description
POST	/api/v1/rooms	Create new collaboration room
GET	/api/v1/rooms/:roomId	Get room details + latest document
PATCH	/api/v1/rooms/:roomId/close	Close room (irreversible)
PATCH	/api/v1/rooms/:roomId/language	Change programming language

WebSocket Events

Event	Direction	Description
connect/disconnect	Client -> Server	User join/leave room
room-close-notification	Server -> Client	Broadcast room closure
language-change-notification	Server -> Client	Broadcast language change

Notes

• Dockerized service and Github Actions CI/CD pipeline
• Dual port exposure (HTTP:8003, WebSocket:8004)
• Y-MongoDB provider for document persistence
• Y.js documents for Monaco Code Editor (can be switched to other code editor libraries depending on our Front End)
• Rooms are closed automatically after period of inactivity (i.e. no connected clients for 10 minutes)

Things to do next after this PR

• Integrate collaboration service into front end.
• Add authentication

[DanielJames0302]

LGTM !