Add React frontend for energy trading system

Implements React + TypeScript UI with Vite and Tailwind CSS.
Features dashboard with real-time WebSocket updates, backtesting
page, model management interface, trading controls, and settings.
Includes state management with Zustand, API integration with
Axios/TanStack Query, and interactive charts with Recharts.

frontend/postcss.config.js

@@ -0,0 +1,6 @@
+export default {
+  plugins: {
+    tailwindcss: {},
+    autoprefixer: {},
+  },
+}