Add Random direction option — picks Buy or Sell once per batch

All accounts in the same batch trade the same resolved direction.
Each new batch (after positions are flat) picks a fresh random direction.

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

app/api/trade/route.ts

@@ -4,7 +4,7 @@ import { POINT_VALUES } from '@/lib/trading-logic';
 
 export async function POST(req: NextRequest) {
     try {
-        const body = await req.json() as { action: 'Buy' | 'Sell'; symbol: string };
+        const body = await req.json() as { action: 'Buy' | 'Sell' | 'Random'; symbol: string };
         const { action, symbol } = body;
 
         if (!action || !symbol) {