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/src/lib/utils.ts

@@ -0,0 +1,28 @@
+import { type ClassValue, clsx } from 'clsx';
+
+export function cn(...inputs: ClassValue[]) {
+  return clsx(inputs);
+}
+
+export function formatDate(date: string | Date): string {
+  const d = new Date(date);
+  return d.toLocaleString();
+}
+
+export function formatCurrency(value: number, currency: string = 'EUR'): string {
+  return new Intl.NumberFormat('en-EU', {
+    style: 'currency',
+    currency,
+  }).format(value);
+}
+
+export function formatNumber(value: number, decimals: number = 2): string {
+  return new Intl.NumberFormat('en-EU', {
+    minimumFractionDigits: decimals,
+    maximumFractionDigits: decimals,
+  }).format(value);
+}
+
+export function formatPercentage(value: number, decimals: number = 2): string {
+  return `${formatNumber(value * 100, decimals)}%`;
+}