Add Prettier for TypeScript formatting

- Install prettier
- Configure .prettierrc.json and .prettierignore
- Add npm scripts: format, format:check
- Add Makefile target: format-frontend
- Format all frontend files

frontend/app/page.tsx

@@ -15,7 +15,8 @@ export default function Home() {
 
   useEffect(() => {
     if (user && isAuthorized) {
-      api.get<{ value: number }>("/api/counter")
+      api
+        .get<{ value: number }>("/api/counter")
         .then((data) => setCount(data.value))
         .catch(() => setCount(null));
     }