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/email.py

@@ -148,8 +148,12 @@ def smtp_test():
         "</body></html>"
     )
 
-    # Try Graph API first
-    if state.connector and state.connector.is_authenticated():
+    # Try Graph API first — unless the user opted to always use SMTP. Graph
+    # returns 202 (queued) even for recipients Exchange later silently drops
+    # (e.g. a Google-hosted subdomain of the O365 domain), so SMTP is the only
+    # reliable path for those; prefer_smtp forces it.
+    prefer_smtp = bool(saved.get("prefer_smtp"))
+    if state.connector and state.connector.is_authenticated() and not prefer_smtp:
         try:
             _send_email_graph(subject, body_html, recipients)
             return jsonify({"ok": True, "method": "graph", "recipients": recipients})
@@ -285,8 +289,8 @@ def send_report():
         "</body></html>"
     )
 
-    # Try Graph API first
-    if state.connector and state.connector.is_authenticated():
+    # Try Graph API first — unless prefer_smtp is set (see smtp_test for why).
+    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)