Stop flagging SEPA members with a running Rücklastschrift-Mahnung as overdue

sepa_debit_overdue fired unconditionally for every overdue SEPA claim past the
grace period, regardless of whether a reminder had already been sent for it --
so a Rücklastschrift-Mahnung created via the reminder mechanism made no
difference to the housekeeper output. Check for an already-sent reminder whose
own payment deadline hasn't expired yet first; if there is one, show a
low-priority "Rücklastschriftklärung läuft" note instead, mirroring the
non-SEPA "reminder_awaiting_deadline" fix. Once that deadline passes without
resolution, the plain sepa_debit_overdue notice returns.

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

tests/test_reminders.py

@@ -152,6 +152,47 @@ def test_sepa_member_gets_debit_followup_instead_of_reminder(tmp_path) -> None:
     assert "SEPA" in sepa_finding.detail
 
 
+def test_sepa_member_with_running_reminder_shows_awaiting_note_not_overdue(tmp_path) -> None:
+    repository, member = _overdue_claim_repository(tmp_path)
+    member.iban = "DE89370400440532013000"
+    member.mandate_reference = "MANDATE-1"
+    member.mandate_signed_at = "2026-01-01"
+    member.mandate_active = True
+    repository.save_member(member)
+    housekeeper = Housekeeper(repository)
+
+    draft = repository.create_reminder_draft(
+        member.member_id,
+        "claim-1",
+        level=1,
+        name="Rücklastschrift",
+        payment_deadline_days=14,
+        items=[{"description": "Rücklastschriftgebühr", "amount": "5.00"}],
+    )
+    sent = repository.mark_reminder_sent(member.member_id, "claim-1", draft["reminder_id"])
+    deadline = date.fromisoformat(sent["payment_deadline"])
+
+    findings = [
+        item
+        for item in housekeeper.run(today=deadline - timedelta(days=1))
+        if item.member_id == member.member_id
+    ]
+
+    assert not any(item.code == "sepa_debit_overdue" for item in findings)
+    awaiting = next(item for item in findings if item.code == "sepa_debit_awaiting_deadline")
+    assert awaiting.severity == "info"
+    assert "Rücklastschrift" in awaiting.title
+
+    # Once the reminder's own deadline has passed without resolution, the plain SEPA
+    # follow-up notice returns so it doesn't just silently go quiet forever.
+    findings = [
+        item for item in housekeeper.run(today=deadline + timedelta(days=1))
+        if item.member_id == member.member_id
+    ]
+    assert any(item.code == "sepa_debit_overdue" for item in findings)
+    assert not any(item.code == "sepa_debit_awaiting_deadline" for item in findings)
+
+
 def test_draft_can_be_cancelled_but_sent_reminder_cannot(tmp_path) -> None:
     repository, member = _overdue_claim_repository(tmp_path)
     draft = repository.create_reminder_draft(