Fix portfolio ID validation to accept Wren API portfolio IDs

Changed backend validation from hardcoded [1, 2, 3] to accept any positive
integer portfolio ID. The Wren API returns portfolios with their real IDs
(not limited to 1-3), so the backend needs to accept dynamic portfolio IDs.

- Changed validation to check for positive integers instead of [1, 2, 3]
- Added logging to show which portfolio ID is being processed
- Pricing calculation already has fallback to $18/ton for unknown IDs

This fixes the "Invalid portfolio ID" error when trying to checkout.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

server/routes/checkout.js

@@ -47,10 +47,14 @@ router.post('/create-session', async (req, res) => {
       return res.status(400).json({ error: 'Invalid tons value' });
     }
 
-    if (!portfolioId || ![1, 2, 3].includes(portfolioId)) {
+    // Accept any valid positive integer portfolio ID (from Wren API)
+    if (!portfolioId || !Number.isInteger(portfolioId) || portfolioId <= 0) {
+      console.error('❌ Invalid portfolio ID received:', portfolioId);
       return res.status(400).json({ error: 'Invalid portfolio ID' });
     }
 
+    console.log(`📦 Creating checkout for portfolio ID: ${portfolioId}, tons: ${tons}`);
+
     // Calculate pricing
     const { baseAmount, processingFee, totalAmount, pricePerTon } = calculatePricing(tons, portfolioId);