feat(sprint1-step2): core economy TS + useEconomy hook (lazy calc) + 13 tests vitest

Frontend/vite.config.js

@@ -1,7 +1,9 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 
-// https://vitejs.dev/config/
 export default defineConfig({
   plugins: [react()],
+  test: {
+    environment: 'node',
+  },
 })