feat: implement AuthModule with authentication and RBAC features

Added AuthModule with services, controllers, and guards for authentication. Implements session management, role-based access control, 2FA, and DTOs for user login, registration, and token refresh.

backend/src/auth/guards/roles.guard.ts

@@ -0,0 +1,28 @@
+import { CanActivate, ExecutionContext, Injectable } from "@nestjs/common";
+import { Reflector } from "@nestjs/core";
+import { RbacService } from "../rbac.service";
+
+@Injectable()
+export class RolesGuard implements CanActivate {
+	constructor(
+		private reflector: Reflector,
+		private rbacService: RbacService,
+	) {}
+
+	async canActivate(context: ExecutionContext): Promise<boolean> {
+		const requiredRoles = this.reflector.getAllAndOverride<string[]>("roles", [
+			context.getHandler(),
+			context.getClass(),
+		]);
+		if (!requiredRoles) {
+			return true;
+		}
+		const { user } = context.switchToHttp().getRequest();
+		if (!user) {
+			return false;
+		}
+
+		const userRoles = await this.rbacService.getUserRoles(user.sub);
+		return requiredRoles.some((role) => userRoles.includes(role));
+	}
+}