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_sepa.py

@@ -290,3 +290,101 @@ def test_generated_mail_send_mode_reuses_one_smtp_connection_for_batch(tmp_path,
     assert generated[0].archive_path.is_file()
     assert len(connections_opened) == 1, "one connection should be reused for the whole batch"
     assert len(sent) == len(debits)
+
+
+def test_generated_mail_send_mode_copies_to_sent_folder_reusing_one_imap_connection(
+    tmp_path, monkeypatch
+):
+    import ccma.services.sepa_mail as sepa_mail_module
+
+    repository, ada = _repository(tmp_path)
+    second = repository.create_member(first_name="Grace", last_name="Hopper", member_number="C3-43")
+    second.status = "active"
+    second.email = "grace@example.org"
+    second.account_holder = "Grace Hopper"
+    second.iban = "DE89370400440532013000"
+    second.bic = "COBADEFFXXX"
+    second.mandate_reference = "MANDAT-43"
+    second.mandate_signed_at = "2025-01-10"
+    second.mandate_active = True
+    repository.save_member(second)
+    repository.save_contributions(
+        second.member_id,
+        ContributionData(
+            claims=[
+                {
+                    "claim_id": "due",
+                    "title": "Mitgliedsbeitrag 2026",
+                    "amount": "150.00",
+                    "due_date": "2026-01-31",
+                    "status": "open",
+                }
+            ]
+        ),
+    )
+    organization = repository.get_configuration()["organization"]
+    organization.update(
+        {
+            "name": "Chaos Computer Club Mannheim e.V.",
+            "email": "verwaltung@example.org",
+            "iban": "DE89370400440532013000",
+            "bic": "COBADEFFXXX",
+            "creditor_id": "DE98ZZZ09999999999",
+        }
+    )
+    repository.save_organization(organization)
+    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",
+    )
+    debits, _warnings = pending_direct_debits(repository, due_until=date(2026, 12, 31))
+    assert len(debits) == 2
+
+    monkeypatch.setattr(
+        sepa_mail_module, "smtp_session", contextmanager(lambda settings: iter(["smtp-client"]))
+    )
+    monkeypatch.setattr(sepa_mail_module, "send_via_smtp", lambda client, content: None)
+    imap_connections = []
+
+    @contextmanager
+    def fake_imap_session(settings):
+        imap_connections.append(settings)
+        yield "imap-client"
+
+    monkeypatch.setattr(sepa_mail_module, "imap_session", fake_imap_session)
+    ensured = []
+    appended = []
+    monkeypatch.setattr(
+        sepa_mail_module, "ensure_imap_folder", lambda client, folder: ensured.append(folder)
+    )
+    monkeypatch.setattr(
+        sepa_mail_module,
+        "append_message",
+        lambda client, content, *, folder, flags: appended.append((client, folder, flags)),
+    )
+
+    generate_debit_mails(
+        repository,
+        debits,
+        collection_date=date(2026, 8, 3),
+        delivery_mode="send",
+        sender_name="Verwaltung C3MA",
+        sender_email="verwaltung@example.org",
+        signature="Der Vorstand",
+    )
+
+    assert len(imap_connections) == 1, "one IMAP connection should be reused for the whole batch"
+    assert ensured == ["INBOX.Gesendet"]
+    assert appended == [("imap-client", "INBOX.Gesendet", r"(\Seen)")] * 2