Add ticket +/- quantity support to shared contracts and services

- Add ticket_type_id field to TicketDTO for grouping
- Add adjust_ticket_quantity to CalendarService protocol + SQL impl
- Add stub for adjust_ticket_quantity

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

contracts/dtos.py

@@ -56,6 +56,7 @@ class TicketDTO:
     created_at: datetime | None = None
     checked_in_at: datetime | None = None
     entry_id: int | None = None
+    ticket_type_id: int | None = None
     price: Decimal | None = None
     order_id: int | None = None
     calendar_container_id: int | None = None