Add "prefer SMTP" toggle to skip Microsoft Graph for email

When the M365 connector is connected the app always tries Graph first,
and a Graph 202 ends the send — so report mail to recipients Exchange
silently drops (Google-hosted subdomains of the O365 domain) never
reaches them, even with working SMTP configured.

New prefer_smtp flag gates all three Graph branches (smtp_test,
send_report, _maybe_send_auto_email) so they go straight to SMTP. UI
toggle #st-smtpPreferSmtp in Settings → E-mailrapport, saved/loaded by
scheduler.js, with da/de/en strings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

routes/scan.py

@@ -54,7 +54,7 @@ def _maybe_send_auto_email():
             "</body></html>"
         )
 
-        if state.connector and state.connector.is_authenticated():
+        if state.connector and state.connector.is_authenticated() and not smtp_cfg.get("prefer_smtp"):
             try:
                 _send_email_graph(subject, body_html, recipients,
                                   attachment_bytes=xl_bytes, attachment_name=fname)