feat: scaffold Flask + React app with schema and JSON error handling

Claude-Session: https://claude.ai/code/session_01M9MLit5Ko3X4s7rzC5Kv7X

vite.config.ts

@@ -0,0 +1,14 @@
+/// <reference types="vitest/config" />
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+import tailwindcss from '@tailwindcss/vite'
+
+export default defineConfig({
+  plugins: [react(), tailwindcss()],
+  server: { proxy: { '/api': 'http://127.0.0.1:5000' } },
+  test: {
+    environment: 'jsdom',
+    setupFiles: ['./src/test/setup.ts'],
+    unstubGlobals: true,
+  },
+})