Fix housekeeper false-positive overdue errors and ended-member birthday/anniversary noise

An overdue claim whose reminder had already been sent, with that reminder's own
payment deadline still running, fell through to the plain "überfällig" error
finding whenever reminder_due's escalation check returned None to signal "not
yet time for the next Mahnstufe" -- that None was indistinguishable from "never
handled at all" to the caller, so it looked neglected even though a reminder was
already out. Give that case its own low-priority "reminder_awaiting_deadline"
finding instead of silently falling back to the overdue-error path.

Birthday and membership-anniversary findings also kept firing for members whose
status is "ended", which doesn't make sense once the membership itself is over.

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

tests/test_reminders.py

@@ -61,6 +61,35 @@ def test_reminder_rule_progresses_only_after_sent_deadline(tmp_path) -> None:
     assert "Erste Mahnung" in next_task.title
 
 
+def test_overdue_claim_awaiting_reminder_deadline_is_not_reported_as_error(tmp_path) -> None:
+    repository, member = _overdue_claim_repository(tmp_path)
+    housekeeper = Housekeeper(repository)
+    draft = repository.create_reminder_draft(
+        member.member_id,
+        "claim-1",
+        level=1,
+        name="Zahlungserinnerung",
+        payment_deadline_days=14,
+        items=[],
+    )
+    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
+    ]
+
+    # A reminder was already sent and its own deadline hasn't expired yet -- this is
+    # being handled, so it must not appear as an unaddressed "error"-severity overdue
+    # claim, only as a low-priority note that the existing deadline is still running.
+    assert not any(item.code == "claim_overdue" for item in findings)
+    awaiting = next(item for item in findings if item.code == "reminder_awaiting_deadline")
+    assert awaiting.severity == "info"
+    assert "Zahlungserinnerung" in awaiting.title
+
+
 def test_dunning_hold_suppresses_and_then_restores_task(tmp_path) -> None:
     repository, member = _overdue_claim_repository(tmp_path)
     housekeeper = Housekeeper(repository)