chore(01-01): install vitest test infrastructure

- Add vitest, @testing-library/react, @testing-library/jest-dom, @testing-library/user-event, jsdom
- Configure vite.config.ts with jsdom test environment and globals
- Add test-setup.ts importing jest-dom matchers

frontend/vite.config.ts

@@ -1,3 +1,4 @@
+/// <reference types="vitest" />
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
@@ -18,4 +19,9 @@ export default defineConfig({
       },
     },
   },
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: ['./src/test-setup.ts'],
+  },
 })