Add thank you page and fix webhook stock update

- Create thank you page template with bilingual content (FR/EN)
- Add automatic redirect to /thanks after successful payment
- Fix webhook: move kirby()->impersonate() before product update
- Add error handling in webhook with try-catch
- Pass order token to thank you page for future enhancements
- Update thank you page styling for better UX

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

assets/js/snipcart.js

@@ -4,6 +4,13 @@ window.SnipcartSettings = {
   loadStrategy: 'on-user-interaction',
 };
 
+// Redirection après paiement réussi
+document.addEventListener('snipcart.ready', function() {
+  Snipcart.execute('bind', 'order.completed', function(order) {
+    window.location.href = '/thanks?order=' + order.token;
+  });
+});
+
 (() => {
   var c, d;
   (d = (c = window.SnipcartSettings).version) != null || (c.version = '3.0');