Fix ticket_types lazy-load in async: add lazy=selectin

CalendarEntry.ticket_types used default lazy loading which triggers
MissingGreenlet in async context when accessed in templates.

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

models/calendars.py

@@ -129,6 +129,7 @@ class CalendarEntry(Base):
         cascade="all, delete-orphan",
         passive_deletes=True,
         order_by="TicketType.name",
+        lazy="selectin",
     )
 
 DAY_LABELS = [