[BE-01] Implement WebSocket gateway for real-time notifications

[yusuftomilola]

Overview

The notifications/gateway/notifications.gateway.ts file exists but is unimplemented — notifications are REST-poll-only. Members miss time-sensitive updates (booking confirmations, payment events) without a manual page refresh.

Context

• NotificationType enum: backend/src/notifications/enums/notification-type.enum.ts
• CreateNotificationProvider: backend/src/notifications/providers/create-notification.provider.ts — persists notifications via REST
• Gateway file already scaffolded at: backend/src/notifications/gateway/notifications.gateway.ts
• @nestjs/websockets and socket.io are available in the NestJS ecosystem

Tasks

• Implement @WebSocketGateway() with CORS config in notifications.gateway.ts
• handleConnection() authenticates the socket via JWT from the handshake Authorization header; disconnect unauthenticated sockets immediately
• handleDisconnect() removes the socket from the user's room
• Add notifyUser(userId, payload) method that emits to a user-specific room (e.g. room:${userId})
• Call notifyUser() from CreateNotificationProvider after persisting each notification to the database
• Register the gateway as a provider in NotificationsModule

Files to Modify / Create

• backend/src/notifications/gateway/notifications.gateway.ts
• backend/src/notifications/notifications.module.ts
• backend/src/notifications/providers/create-notification.provider.ts

[Emelie-Dev]

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[nottherealalanturing]

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[alade-dev]

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[grantfox-oss]

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@nottherealalanturing's PR #1250 was approved and merged by @yusuftomilola.

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