test(media): fix type casting in MediaController unit tests

Update type casting for `Response` object in MediaController tests to use `unknown as Response` for stricter type safety. Remove unused `s3Service` variable for cleanup.

backend/src/media/media.controller.spec.ts

@@ -1,12 +1,12 @@
 import { Readable } from "node:stream";
 import { NotFoundException } from "@nestjs/common";
 import { Test, TestingModule } from "@nestjs/testing";
+import type { Response } from "express";
 import { S3Service } from "../s3/s3.service";
 import { MediaController } from "./media.controller";
 
 describe("MediaController", () => {
 	let controller: MediaController;
-	let s3Service: S3Service;
 
 	const mockS3Service = {
 		getFileInfo: jest.fn(),
@@ -20,7 +20,6 @@ describe("MediaController", () => {
 		}).compile();
 
 		controller = module.get<MediaController>(MediaController);
-		s3Service = module.get<S3Service>(S3Service);
 	});
 
 	it("should be defined", () => {
@@ -31,7 +30,7 @@ describe("MediaController", () => {
 		it("should stream the file and set headers with path containing slashes", async () => {
 			const res = {
 				setHeader: jest.fn(),
-			} as any;
+			} as unknown as Response;
 			const stream = new Readable();
 			stream.pipe = jest.fn();
 			const key = "contents/user-id/test.webp";
@@ -52,7 +51,7 @@ describe("MediaController", () => {
 
 		it("should throw NotFoundException if file is not found", async () => {
 			mockS3Service.getFileInfo.mockRejectedValue(new Error("Not found"));
-			const res = {} as any;
+			const res = {} as unknown as Response;
 
 			await expect(controller.getFile("invalid", res)).rejects.toThrow(
 				NotFoundException,