Add WebSocket Gateway for Real-Time Session Events

[Mkalbani]

Description

Introduce a WebSocket gateway so that clients receive real-time updates during an active puzzle session — hint reveals, score changes, time warnings, and completion events — without polling. This dramatically improves the game feel and sets the foundation for future real-time multiplayer or live leaderboard features.

Acceptance Criteria

• A NestJS @WebSocketGateway is configured under src/gateway/
• Clients authenticate the WebSocket connection using their JWT
• A session:joined event is emitted when a player starts a session
• A session:score_update event is emitted whenever score changes
• A session:hint_revealed event is emitted when a hint is requested
• A session:completed event is emitted with final score on puzzle solve
• A session:time_warning event fires at configurable time thresholds
• Clients are placed in a per-session room and only receive events for their own session
• Unit tests cover connection auth, room assignment, and event emission

[Nemenwa]

Hi maintainer, I have reviewed the task description and will like to work on this issue please. I can finsih in 6hours, THank you

[Primex-hub]

I would love to solve this issue and I can submit within 24hrs

[grantfox-oss]

🦊 GrantFox — @Nemenwa has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #72)
2. Your PR will be reviewed by the MindFlowInteractive maintainers

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