fix: Remove fallback that breaks TP2-as-runner system

- Change tp2SizePercent fallback from || 100 to ?? 0
- Allows 0 value to pass through (means 'activate trailing stop, don't close')
- Fixes bug where TP2 was closing 100% of remaining position
- Now correctly leaves 25% runner after TP1 closes 75%
- Applied to both execute and test endpoints

app/api/trading/test/route.ts

@@ -258,8 +258,8 @@ export async function POST(request: NextRequest): Promise<NextResponse<TestTrade
         tp1Price,
         tp2Price,
         stopLossPrice,
-        tp1SizePercent: config.takeProfit1SizePercent || 50,
-        tp2SizePercent: config.takeProfit2SizePercent || 100,
+        tp1SizePercent: config.takeProfit1SizePercent ?? 75,
+        tp2SizePercent: config.takeProfit2SizePercent ?? 0, // 0 = activate trailing stop, don't close
         direction: direction,
         // Dual stop parameters
         useDualStops: config.useDualStops,