Move auth server from federation to account

Account is now the OAuth authorization server with magic link login,
OAuth2 authorize endpoint, SSO logout, and session management.

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

events/models/__init__.py

@@ -0,0 +1,4 @@
+from .calendars import (
+    Calendar, CalendarEntry, CalendarSlot,
+    TicketType, Ticket, CalendarEntryPost,
+)

events/models/calendars.py

@@ -0,0 +1,4 @@
+from shared.models.calendars import (  # noqa: F401
+    Calendar, CalendarEntry, CalendarSlot,
+    TicketType, Ticket, CalendarEntryPost,
+)