feat(messages): integrate UsersModule into MessagesModule with forward-ref

- Added `UsersModule` to `MessagesModule` imports using `forwardRef`.
- Injected `UsersService` into `MessagesService` to support user-related operations.

backend/src/messages/messages.service.ts

@@ -1,4 +1,4 @@
-import { ForbiddenException, Injectable } from "@nestjs/common";
+import { ForbiddenException, forwardRef, Inject, Injectable } from "@nestjs/common";
 import { EventsGateway } from "../realtime/events.gateway";
 import { UsersService } from "../users/users.service";
 import type { CreateMessageDto } from "./dto/create-message.dto";
@@ -9,6 +9,7 @@ export class MessagesService {
 	constructor(
 		private readonly messagesRepository: MessagesRepository,
 		private readonly eventsGateway: EventsGateway,
+		@Inject(forwardRef(() => UsersService))
 		private readonly usersService: UsersService,
 	) {}