feat: Implement AchievementRepository and refactor AchievementService to utilize repository pattern for data access

Author: letnull19A

src/achievement/achievement.module.ts

@@ -1,13 +1,14 @@
 import { Module } from '@nestjs/common';
 import { AchievementService } from './achievement.service';
 import { AchievementController } from './achievement.controller';
+import { AchievementRepository } from './achievement.repository';
 import { DatabaseModule } from '../database/database.module';
 
 @Module({
   imports: [DatabaseModule],
   controllers: [AchievementController],
-  providers: [AchievementService],
-  exports: [AchievementService],
+  providers: [AchievementService, AchievementRepository],
+  exports: [AchievementService, AchievementRepository],
 })
 export class AchievementModule {}