Fix DTO compatibility in cart templates and page_cart service

- page_cart.py: use ce.calendar_container_id instead of ce.calendar.container_id
- _cart.html: use entry.calendar_name instead of entry.calendar.name
- Update shared submodule with DTO field additions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/_types/cart/_cart.html

@@ -43,7 +43,7 @@
                 <li class="flex items-start justify-between text-sm">
                   <div>
                     <div class="font-medium">
-                      {{ entry.name or entry.calendar.name }}
+                      {{ entry.name or entry.calendar_name }}
                     </div>
                     <div class="text-xs text-stone-500">
                       {{ entry.start_at }}