[BE-55] Implement WebSocket notifications gateway for real-time in-app alerts

[yusuftomilola]

Overview

The frontend uses socket.io-client@4.8.3 for real-time communication. In-app notifications (asset transferred to you, work order assigned, maintenance due) must arrive instantly without page refresh. The WebSocket gateway was previously implemented and then deleted in commit be0be8c — it needs to be rebuilt.

Context

• package.json has @nestjs/websockets@10.4.15, @nestjs/platform-socket.io@10.4.15, and socket.io@4.8.1
• The gateway must authenticate the WebSocket connection using the JWT from the handshake auth header
• Each connected user joins a room named user:{userId} so notifications can be sent to specific users

Acceptance Criteria

• Create NotificationsGateway with @WebSocketGateway({ cors: true, namespace: '/notifications' })
• On handleConnection: extract JWT from client.handshake.auth.token, verify with JwtService, join room user:{userId}, disconnect unauthenticated clients
• Create NotificationsService.sendToUser(userId, type, payload) — emits to the user's room: this.server.to(user:${userId}).emit('notification', { type, payload, timestamp })
• Define notification types: ASSET_TRANSFERRED, WORK_ORDER_ASSIGNED, MAINTENANCE_DUE, BOOKING_CONFIRMED, CHECKOUT_OVERDUE, WARRANTY_EXPIRING
• Create Notification entity to persist all sent notifications: id, userId, type, title, body, payload (JSON), isRead, createdAt
• GET /notifications — current user's notification history, unread first
• PATCH /notifications/:id/read and PATCH /notifications/read-all

[walexjnr]

@walexjnr has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi can i work on this task?

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[drips-wave]

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