Actually add the user as attendee on accepted invite

src/api/invitations.py

@@ -228,10 +228,19 @@ async def accept_invitation(invitation_id: PydanticObjectId, user: CurrentUserDe
             detail="You can only accept pending invitations.",
         )
 
+    # Mark the invitation as accepted
     invitation.status = "accepted"
     invitation.responded_at = datetime.now(tz=UTC)
     _ = await invitation.save()
 
+    # Add the user to the event
+    event = invitation.event
+    if isinstance(event, Link):
+        raise UnfetchedLinkError(event)
+
+    event.attendees.append(invitation.invitee)
+    event = await event.replace()
+
     # Send back a notification to the invitor about the acceptance
     notification = Notification(
         user=invitation.invitor,