app controller: move safe mode from app controller to SessionLoader.

app/logical/session_loader.rb

@@ -26,6 +26,7 @@ class SessionLoader
     update_last_logged_in_at
     update_last_ip_addr
     set_time_zone
+    set_safe_mode
     CurrentUser.user.unban! if CurrentUser.user.ban_expired?
     DanbooruLogger.initialize(request, session, CurrentUser.user)
   end
@@ -104,5 +105,9 @@ private
   def set_time_zone
     Time.zone = CurrentUser.user.time_zone
   end
-end
 
+  def set_safe_mode
+    safe_mode = request.host.match?(/safebooru/i) || params[:safe_mode].to_s.truthy? || CurrentUser.user.enable_safe_mode?
+    CurrentUser.safe_mode = safe_mode
+  end
+end