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>

services/stubs.py

@@ -132,6 +132,11 @@ class StubCalendarService:
     ) -> None:
         pass
 
+    async def adjust_ticket_quantity(
+        self, session, entry_id, count, *, user_id, session_id, ticket_type_id=None,
+    ) -> int:
+        return 0
+
     async def entry_ids_for_content(self, session, content_type, content_id):
         return set()