The Bestätigung email was sent via Celery task (fire-and-forget), so the UI
always showed "wird gesendet" even when the task failed silently in the worker.
Now sends synchronously from the web process (matching the working test email
pattern) with proper error display to the user.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
b8fb35db7a