feat: add per-member payment frequencies

src/ccma/storage/repository.py

@@ -29,6 +29,7 @@ from ccma.domain.models import (
     ASSET_OWNER_TYPE_LABELS,
     ASSET_STATUS_LABELS,
     MEMBERSHIP_STATUS_LABELS,
+    PAYMENT_FREQUENCY_LABELS,
     Asset,
     ContributionData,
     Event,
@@ -391,6 +392,8 @@ class MemberRepository:
             raise RepositoryError(
                 "Ein aktives Lastschriftmandat benötigt IBAN, Mandatsreferenz und Erteilungsdatum."
             )
+        if member.payment_frequency not in PAYMENT_FREQUENCY_LABELS:
+            raise RepositoryError("Ungültige Zahlweise.")
         if member.member_number != existing.member_number:
             self._assert_member_number_available(member.member_number, exclude_member_id=member.member_id)
         changes = self._summarize_changes(existing, member)