feat(web): add Next.js portfolio with live MT5 dashboard

- Linear design system (dark canvas, lavender accent)
- Live account stats, open positions, pending orders (30s polling)
- Trade history with equity curve chart
- Backtest results table
- Proxy API routes — MT5_BASE_URL server-side only, never exposed to browser
- Deploy on Vercel: set MT5_BASE_URL env var

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/next-env.d.ts

@@ -0,0 +1,6 @@
+/// <reference types="next" />
+/// <reference types="next/image-types/global" />
+/// <reference path="./.next/types/routes.d.ts" />
+
+// NOTE: This file should not be edited
+// see https://nextjs.org/docs/app/api-reference/config/typescript for more information.