Delete invoice when crypto payment is cancelled

When a crypto payment is cancelled, delete the associated invoice and
line items since no actual purchase occurred. Keep the crypto_payment
record for transaction history and audit trails.

This prevents cancelled quotes from cluttering user purchase history.

make_post_sell/views/crypto.py

@@ -742,6 +742,22 @@ def crypto_cancel(request):
     # Cancel the payment
     crypto_payment.status = CryptoPayment.STATUS_CANCELLED
     request.dbsession.add(crypto_payment)
+    
+    # Delete the invoice since this was never a real purchase
+    # Keep the crypto_payment for transaction history
+    invoice = crypto_payment.invoice
+    if invoice:
+        # Delete invoice line items first
+        for line_item in invoice.line_items:
+            request.dbsession.delete(line_item)
+        
+        # Clear the invoice reference from crypto payment
+        crypto_payment.invoice_id = None
+        crypto_payment.invoice = None
+        
+        # Delete the invoice
+        request.dbsession.delete(invoice)
+    
     request.dbsession.flush()
 
     # Get the cart URL for redirect