chore: add Vitest + Testing Library test infrastructure

vitest.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from 'vitest/config'
+import react from '@vitejs/plugin-react'
+import { resolve } from 'path'
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: ['./vitest.setup.ts'],
+  },
+  resolve: {
+    alias: {
+      '@': resolve(__dirname, '.'),
+    },
+  },
+})

vitest.setup.ts

@@ -0,0 +1 @@
+import '@testing-library/jest-dom'