Fix custom calculator type: use monetary amount instead of CO₂ tons

Critical fix: The 'custom' calculation type should represent monetary amount
(USD) to spend on carbon offsets, not tons of CO₂. The calculator converts
money to CO₂, not the other way around.

Changes:
- Update test page label from "Custom Amount (tons CO₂)" to "Custom Amount (USD)"
- Add helper text explaining calculator converts money to CO₂
- Update description function to show "$100 USD" instead of "100 tons CO₂"
- Change default/preset values to realistic dollar amounts ($50 default, $100 preset)

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

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

app/qr-test/page.tsx

@@ -12,7 +12,7 @@ export default function QRTestPage() {
   const [fuelRate, setFuelRate] = useState('100');
   const [fuelAmount, setFuelAmount] = useState('500');
   const [fuelUnit, setFuelUnit] = useState<'liters' | 'gallons'>('liters');
-  const [customAmount, setCustomAmount] = useState('5');
+  const [customAmount, setCustomAmount] = useState('50');
   const [vesselName, setVesselName] = useState('');
   const [imo, setImo] = useState('');
 
@@ -38,7 +38,7 @@ export default function QRTestPage() {
     },
     custom: {
       calculationType: 'custom' as const,
-      customAmount: 5,
+      customAmount: 100,
     },
   };
 
@@ -284,14 +284,18 @@ export default function QRTestPage() {
             {calculationType === 'custom' && (
               <div className="mb-6">
                 <label className="block text-sm font-medium text-gray-700 mb-2">
-                  Custom Amount (tons CO₂)
+                  Custom Amount (USD)
                 </label>
                 <input
                   type="number"
                   value={customAmount}
                   onChange={(e) => setCustomAmount(e.target.value)}
+                  placeholder="e.g., 100"
                   className="w-full px-4 py-2 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
                 />
+                <p className="mt-1 text-xs text-gray-500">
+                  Monetary amount to spend on carbon offsets (calculator will convert to CO₂)
+                </p>
               </div>
             )}
 

src/utils/qrDataValidator.ts

@@ -165,7 +165,7 @@ export function getQRDataDescription(data: QRCalculatorData): string {
     case 'distance':
       return `Distance-based: ${data.distance} nm at ${data.speed} knots`;
     case 'custom':
-      return `Custom: ${data.customAmount} tons CO₂`;
+      return `Custom: $${data.customAmount} USD`;
     default:
       return 'Unknown calculation type';
   }