Add ticket-to-cart integration

Reserved tickets now flow through the cart and checkout pipeline:
- TicketDTO gains price, entry_id, order_id, calendar_container_id
- CartSummaryDTO gains ticket_count, ticket_total
- 6 new CalendarService methods for ticket lifecycle
- cart_summary includes tickets; login adoption migrates tickets
- New _ticket_items.html template for checkout return page

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

services/cart_impl.py

@@ -93,6 +93,23 @@ class SqlCartService:
         calendar_count = len(cal_entries)
         calendar_total = sum(Decimal(str(e.cost or 0)) for e in cal_entries if e.cost is not None)
 
+        # --- tickets ---
+        if page_post_id is not None:
+            tickets = await services.calendar.tickets_for_page(
+                session, page_post_id,
+                user_id=user_id,
+                session_id=session_id,
+            )
+        else:
+            tickets = await services.calendar.pending_tickets(
+                session,
+                user_id=user_id,
+                session_id=session_id,
+            )
+
+        ticket_count = len(tickets)
+        ticket_total = sum(Decimal(str(t.price or 0)) for t in tickets)
+
         items = [_item_to_dto(ci) for ci in cart_items]
 
         return CartSummaryDTO(
@@ -101,6 +118,8 @@ class SqlCartService:
             calendar_count=calendar_count,
             calendar_total=calendar_total,
             items=items,
+            ticket_count=ticket_count,
+            ticket_total=ticket_total,
         )
 
     async def cart_items(