test(backend): migrate to vitest (#95)

Use `vitest` for backend tests:

- `bench` script now uses [vitest's
`bench`](https://vitest.dev/api/#bench)
- e2e test fails with same error happening now with jest:`data-testid`
attribute not present.
  vitest left, jest right
<img width="1264" height="603" alt="image"
src="https://github.com/user-attachments/assets/56fc43a6-e143-4208-bf14-7e016aae7fa9"
/>

apps/backend/tests/renderRepoCard.test.js

@@ -1,11 +1,12 @@
-import { describe, expect, it } from "@jest/globals";
 import { queryByTestId } from "@testing-library/dom";
-import "@testing-library/jest-dom";
 import { cssToObject } from "@uppercod/css-to-object";
+import { describe, expect, it } from "vitest";
 
 import { renderRepoCard } from "../src/cards/repo.js";
 import { themes } from "../themes/index.js";
 
+import "@testing-library/jest-dom/vitest";
+
 const data_repo = {
   repository: {
     nameWithOwner: "anuraghazra/convoychat",