Change processing fee from 5% to 3%

## Changes Made:

### Backend (server/routes/checkout.js):
- Changed PROCESSING_FEE_PERCENT from 0.05 to 0.03
- Now calculates 3% fee instead of 5%

### Frontend (src/pages/CheckoutSuccess.tsx):
- Updated display text from "Processing Fee (5%)" to "Processing Fee (3%)"
- Receipt now shows correct percentage

## Impact:
- All new orders will have 3% processing fee
- Calculation, display, and Stripe charges all consistent at 3%

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

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

server/routes/checkout.js

@@ -12,7 +12,7 @@ const PORTFOLIO_PRICING = {
 };
 
 // Processing fee percentage
-const PROCESSING_FEE_PERCENT = 0.05; // 5%
+const PROCESSING_FEE_PERCENT = 0.03; // 3%
 
 /**
  * Calculate pricing with processing fee

src/pages/CheckoutSuccess.tsx

@@ -233,7 +233,7 @@ export default function CheckoutSuccess({
                     </span>
                   </div>
                   <div className="flex justify-between items-center">
-                    <span className="text-slate-700">Processing Fee (5%)</span>
+                    <span className="text-slate-700">Processing Fee (3%)</span>
                     <span className="text-slate-900 font-semibold">
                       ${formatCurrency(processingFee)}
                     </span>