fix: break circular dependency between Events↔Sisters↔Activity

- Replace EventsGateway direct dependency in ActivityService with EventEmitter2
- ActivityModule no longer imports EventsModule (cycle broken)
- Register EventEmitterModule in AppModule
- Update activity.service.spec.ts to provide EventEmitter2
- SistersModule safely imports ActivityModule without creating a cycle

Dependency graph after fix:
  EventsModule → SistersModule → ActivityModule (leaf, no back-edge)

backend/package-lock.json

@@ -12,6 +12,7 @@
         "@nestjs/common": "^11.0.1",
         "@nestjs/config": "^4.0.3",
         "@nestjs/core": "^11.0.1",
+        "@nestjs/event-emitter": "^3.0.1",
         "@nestjs/jwt": "^11.0.2",
         "@nestjs/passport": "^11.0.5",
         "@nestjs/platform-express": "^11.0.1",
@@ -2294,6 +2295,19 @@
         }
       }
     },
+    "node_modules/@nestjs/event-emitter": {
+      "version": "3.0.1",
+      "resolved": "https://registry.npmjs.org/@nestjs/event-emitter/-/event-emitter-3.0.1.tgz",
+      "integrity": "sha512-0Ln/x+7xkU6AJFOcQI9tIhUMXVF7D5itiaQGOyJbXtlAfAIt8gzDdJm+Im7cFzKoWkiW5nCXCPh6GSvdQd/3Dw==",
+      "license": "MIT",
+      "dependencies": {
+        "eventemitter2": "6.4.9"
+      },
+      "peerDependencies": {
+        "@nestjs/common": "^10.0.0 || ^11.0.0",
+        "@nestjs/core": "^10.0.0 || ^11.0.0"
+      }
+    },
     "node_modules/@nestjs/jwt": {
       "version": "11.0.2",
       "resolved": "https://registry.npmjs.org/@nestjs/jwt/-/jwt-11.0.2.tgz",
@@ -6204,6 +6218,12 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/eventemitter2": {
+      "version": "6.4.9",
+      "resolved": "https://registry.npmjs.org/eventemitter2/-/eventemitter2-6.4.9.tgz",
+      "integrity": "sha512-JEPTiaOt9f04oa6NOkc4aH+nVp5I3wEjpHbIPqfgCdD5v5bUzy7xQqwcVO2aDQgOWhI28da57HksMrzK9HlRxg==",
+      "license": "MIT"
+    },
     "node_modules/events": {
       "version": "3.3.0",
       "resolved": "https://registry.npmjs.org/events/-/events-3.3.0.tgz",

backend/package.json

@@ -27,6 +27,7 @@
     "@nestjs/common": "^11.0.1",
     "@nestjs/config": "^4.0.3",
     "@nestjs/core": "^11.0.1",
+    "@nestjs/event-emitter": "^3.0.1",
     "@nestjs/jwt": "^11.0.2",
     "@nestjs/passport": "^11.0.5",
     "@nestjs/platform-express": "^11.0.1",

backend/src/activity/activity.module.ts

@@ -2,10 +2,9 @@ import { Module } from '@nestjs/common';
 import { ActivityController } from './activity.controller';
 import { ActivityService } from './activity.service';
 import { PrismaModule } from '../prisma/prisma.module';
-import { EventsModule } from '../events/events.module';
 
 @Module({
-  imports: [PrismaModule, EventsModule],
+  imports: [PrismaModule],
   controllers: [ActivityController],
   providers: [ActivityService],
   exports: [ActivityService],

backend/src/activity/activity.service.spec.ts

@@ -1,4 +1,5 @@
 import { Test, TestingModule } from '@nestjs/testing';
+import { EventEmitter2 } from '@nestjs/event-emitter';
 import { ActivityService } from './activity.service';
 import { PrismaService } from '../prisma/prisma.service';
 
@@ -20,6 +21,7 @@ describe('ActivityService', () => {
       providers: [
         ActivityService,
         { provide: PrismaService, useValue: mockPrisma },
+        EventEmitter2,
       ],
     }).compile();
 

backend/src/activity/activity.service.ts

@@ -1,6 +1,6 @@
-import { Injectable, Optional } from '@nestjs/common';
+import { Injectable } from '@nestjs/common';
+import { EventEmitter2 } from '@nestjs/event-emitter';
 import { PrismaService } from '../prisma/prisma.service';
-import { EventsGateway } from '../events/events.gateway';
 
 export interface LogActivityDto {
   sisterId?: number;
@@ -34,7 +34,7 @@ function sanitizeActivityDetail(detail?: string | null): string | undefined {
 export class ActivityService {
   constructor(
     private readonly prisma: PrismaService,
-    @Optional() private readonly events?: EventsGateway,
+    private readonly eventEmitter: EventEmitter2,
   ) {}
 
   async log(dto: LogActivityDto) {
@@ -49,9 +49,7 @@ export class ActivityService {
       },
     });
 
-    if (this.events) {
-      this.events.broadcastActivity(record);
-    }
+    this.eventEmitter.emit('activity.logged', record);
 
     return record;
   }

backend/src/app.module.ts

@@ -1,5 +1,6 @@
 import { Module } from '@nestjs/common';
 import { ConfigModule } from '@nestjs/config';
+import { EventEmitterModule } from '@nestjs/event-emitter';
 import { ThrottlerModule } from '@nestjs/throttler';
 import { AppController } from './app.controller';
 import { AppService } from './app.service';
@@ -22,6 +23,7 @@ import { DashboardModule } from './dashboard/dashboard.module';
 @Module({
   imports: [
     ConfigModule.forRoot({ isGlobal: true }),
+    EventEmitterModule.forRoot(),
     ThrottlerModule.forRoot([{ ttl: 60000, limit: 100 }]),
     PrismaModule,
     SistersModule,