Add a final safety net in redirectToChannel.SendMessage that refuses a
message when ApplicationID == 0, so it can never be stored as an orphaned
message (application_id = 0, not shown, not deletable). Requested in review.
Cover the previously untested error branches around internal-application
back-fill (create/update failures) so patch coverage no longer regresses.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
