feat(auth): implement role-based access control and user management features

backend/src/users/users.service.ts

@@ -20,4 +20,15 @@ export class UsersService {
   updateProfile(id: number, data: { firstName?: string; lastName?: string; email?: string }) {
     return this.prisma.user.update({ where: { id }, data });
   }
+
+  findAll() {
+    return this.prisma.user.findMany({
+      select: { id: true, username: true, email: true, firstName: true, lastName: true, role: true, createdAt: true },
+      orderBy: { username: 'asc' },
+    });
+  }
+
+  setRole(id: number, role: string) {
+    return this.prisma.user.update({ where: { id }, data: { role } });
+  }
 }