Redirect to cart when quote expires on page

- Add 3-second delay redirect to /cart when quote expires while user is on page
- Provides clear navigation path after expiry warning message
- Prevents users from staying on expired quote pages

make_post_sell/templates/crypto_checkout.j2

@@ -306,6 +306,11 @@
                 clearInterval(countdownInterval);
                 countdownInterval = null;
               }
+              
+              // Redirect to cart after 3 seconds when quote expires
+              setTimeout(() => {
+                window.location.href = '/cart';
+              }, 3000);
             } else if (!expiredWarningShown) {
               // Only update countdown if not expired
               const s = Math.floor(ms / 1000);