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/vitest.config.ts

@@ -8,4 +8,3 @@ export default defineConfig({
     include: ["app/**/*.test.{ts,tsx}"],
   },
 });
-