Add configurable e-mail delivery: direct SMTP send or IMAP drafts

Mahnungs- and SEPA-info-mails could previously only be saved as a local .eml
file that still had to be manually imported into Thunderbird. Add a per-store
"E-Mail-Versand" configuration (Optionen -> E-Mail-Versand, stored in
repository.json alongside the rest of the club's settings, since different
stores may use different mailboxes) with four delivery modes:

- "Lokal speichern": today's behaviour, unchanged default for existing stores.
- "Direkt versenden": sends via SMTP.
- "Als Entwurf ablegen": IMAP APPENDs into a configurable drafts folder, so it
  shows up live in whatever mail client is already watching that account.
- "Jedes Mal fragen": prompts once per generation action (not per e-mail --
  a SEPA batch can cover dozens of members) with Senden/Entwürfe/Abbrechen.

New ccma.services.mail_delivery module (smtplib/imaplib, no new dependency)
opens one authenticated connection per batch and reuses it across all
messages instead of reconnecting per recipient. Both "Verbindung testen"
buttons in Options exercise the same connection path used for real delivery.
The archived per-member copy of every generated e-mail is unaffected and
still always written regardless of delivery mode.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_reminder_mail.py

@@ -1,3 +1,4 @@
+from contextlib import contextmanager
 from email.parser import BytesParser
 from email.policy import default
 
@@ -35,6 +36,7 @@ def test_reminder_mail_is_archived_and_marks_reminder_sent(tmp_path):
         member.member_id,
         "claim-1",
         reminder["reminder_id"],
+        delivery_mode="local",
         output_path=export_path,
         sender_name="Verwaltung C3MA",
         sender_email="verwaltung@example.org",
@@ -72,6 +74,7 @@ def test_reminder_mail_includes_fee_in_open_balance(tmp_path):
         member.member_id,
         "claim-1",
         reminder["reminder_id"],
+        delivery_mode="local",
         output_path=tmp_path / "Mahnung.eml",
         sender_name="Verwaltung C3MA",
         sender_email="verwaltung@example.org",
@@ -81,3 +84,56 @@ def test_reminder_mail_includes_fee_in_open_balance(tmp_path):
     message = BytesParser(policy=default).parsebytes(generated.export_path.read_bytes())
     assert "Offener Betrag: 105.00 Euro" in message.get_content()
     assert "Mahngebühr: 5.00 Euro" in message.get_content()
+
+
+def test_reminder_mail_send_mode_delivers_via_smtp_without_local_file(tmp_path, monkeypatch):
+    import ccma.services.reminder_mail as reminder_mail_module
+
+    repository, member = _overdue_claim_repository(tmp_path / "store")
+    member.email = "reminder@example.org"
+    repository.save_member(member)
+    repository.save_email_settings(
+        delivery_mode="send",
+        smtp_host="mail.example.org",
+        smtp_port=587,
+        smtp_security="none",
+        smtp_username="",
+        smtp_password="",
+        imap_host="",
+        imap_port=993,
+        imap_security="ssl",
+        imap_username="",
+        imap_password="",
+        imap_drafts_folder="",
+    )
+    reminder = repository.create_reminder_draft(
+        member.member_id,
+        "claim-1",
+        level=1,
+        name="Zahlungserinnerung",
+        payment_deadline_days=14,
+    )
+
+    sent = []
+    fake_smtp_session = contextmanager(lambda settings: iter([object()]))
+    monkeypatch.setattr(reminder_mail_module, "smtp_session", fake_smtp_session)
+    monkeypatch.setattr(
+        reminder_mail_module, "send_via_smtp", lambda client, content: sent.append(content)
+    )
+
+    generated = generate_and_send_reminder_mail(
+        repository,
+        member.member_id,
+        "claim-1",
+        reminder["reminder_id"],
+        delivery_mode="send",
+        sender_name="Verwaltung C3MA",
+        sender_email="verwaltung@example.org",
+        signature="Der Vorstand",
+    )
+
+    assert generated.export_path is None
+    assert generated.archive_path.is_file()
+    assert len(sent) == 1
+    data = repository.get_contributions(member.member_id)
+    assert data.reminders[0]["status"] == "sent"