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/postcss.config.js

@@ -0,0 +1,6 @@
+module.exports = {
+  plugins: {
+    tailwindcss: {},
+    autoprefixer: {},
+  },
+};