test(frontend): add vitest test suite and apply code formatting

frontend/src/counter.ts

@@ -1,9 +1,9 @@
 export function setupCounter(element: HTMLButtonElement) {
-  let counter = 0
+  let counter = 0;
   const setCounter = (count: number) => {
-    counter = count
-    element.innerHTML = `Count is ${counter}`
-  }
-  element.addEventListener('click', () => setCounter(counter + 1))
-  setCounter(0)
+    counter = count;
+    element.innerHTML = `Count is ${counter}`;
+  };
+  element.addEventListener("click", () => setCounter(counter + 1));
+  setCounter(0);
 }