Copy directly-sent e-mails to an IMAP Sent folder, with a live folder picker

A raw SMTP send has no server-side "Sent" copy on its own (unlike IMAP
drafts, which are inherently server-side) -- add an opt-in checkbox plus a
configurable target folder so directly sent Mahnungen/SEPA-info-mails still
show up in the account's Gesendet/Sent folder like a normal mail client
would leave them. Applies only to "send" delivery; drafts already live on
the server by definition.

Both the Entwürfe- and Gesendet-folder fields are now editable comboboxes:
a new "Ordnerliste laden" button fetches the real folder list from the IMAP
server (needs working credentials first) via LIST, decoding folder names
from modified UTF-7 (RFC 3501) so names like "Entwürfe" render correctly
instead of as "Entw&APw-rfe". Free text still works -- ensure_imap_folder()
creates the folder on first use if it doesn't exist yet, checked once per
batch rather than before every single message.

mail_delivery.append_to_imap_drafts() became the more general
append_message(client, content, folder=, flags=), reused for both the
\Draft and \Seen cases.

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

tests/test_reminder_mail.py

@@ -137,3 +137,66 @@ def test_reminder_mail_send_mode_delivers_via_smtp_without_local_file(tmp_path,
     assert len(sent) == 1
     data = repository.get_contributions(member.member_id)
     assert data.reminders[0]["status"] == "sent"
+
+
+def test_reminder_mail_send_mode_also_copies_to_sent_folder_when_enabled(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="mail.example.org",
+        imap_port=993,
+        imap_security="ssl",
+        imap_username="",
+        imap_password="",
+        imap_drafts_folder="",
+        imap_sent_enabled=True,
+        imap_sent_folder="INBOX.Gesendet",
+    )
+    reminder = repository.create_reminder_draft(
+        member.member_id,
+        "claim-1",
+        level=1,
+        name="Zahlungserinnerung",
+        payment_deadline_days=14,
+    )
+
+    monkeypatch.setattr(
+        reminder_mail_module, "smtp_session", contextmanager(lambda settings: iter(["smtp-client"]))
+    )
+    monkeypatch.setattr(reminder_mail_module, "send_via_smtp", lambda client, content: None)
+    monkeypatch.setattr(
+        reminder_mail_module, "imap_session", contextmanager(lambda settings: iter(["imap-client"]))
+    )
+    ensured = []
+    appended = []
+    monkeypatch.setattr(
+        reminder_mail_module, "ensure_imap_folder", lambda client, folder: ensured.append((client, folder))
+    )
+    monkeypatch.setattr(
+        reminder_mail_module,
+        "append_message",
+        lambda client, content, *, folder, flags: appended.append((client, folder, flags)),
+    )
+
+    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 ensured == [("imap-client", "INBOX.Gesendet")]
+    assert appended == [("imap-client", "INBOX.Gesendet", r"(\Seen)")]