feat(user-preference): restrict playmode update to official modes only

app/router/private/user.py

@@ -320,6 +320,7 @@ async def change_user_preference(
         user_pref.extra = (user_pref.extra or {}) | request.extra
 
     if request.playmode is not None:
+        if request.playmode.is_official():
             current_user.playmode = request.playmode.to_base_ruleset()
         current_user.g0v0_playmode = request.playmode