Handle failed direct debits through the same reminder mechanism

A Rücklastschrift is still the member's own failure to ensure cover or
provide valid bank details, so it belongs in the same escalation ladder
as a regular reminder -- it now occupies whatever level the claim is next
due for, alongside a "Rücklastschrift" preset next to the existing
Mahnstufe presets.

Mahnung vorbereiten no longer lets the board pick a level (it's computed
automatically from what's already been sent, since the sequencing was
already server-enforced) and replaces the single fee field with a small
items table (Beschreibung + Betrag), so a reminder can carry several
charges at once -- e.g. Rücklastschriftgebühr plus Bankgebühr plus Porto
-- each landing on the claim as its own line item instead of one lump
sum under a generic label. The description field offers the configured
standard texts but stays free-editable.

Those standard texts and amounts, plus the dunning levels themselves
(name/fee/deadline), are now configurable from Optionen -> Mahnungen
instead of only being editable by hand-editing repository.json, which
was the case for the whole reminder policy until now. Cleaned up
reminder_fee/failed_debit_fee on contribution rules while at it -- both
were unused leftovers superseded by this.

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

tests/test_reminders.py

@@ -1,7 +1,9 @@
 from datetime import date, timedelta
+from decimal import Decimal
 
 import pytest
 
+from ccma.domain.contributions import claim_total
 from ccma.domain.models import ContributionData
 from ccma.services.housekeeper import Housekeeper
 from ccma.storage.repository import MemberRepository, RepositoryError
@@ -42,7 +44,7 @@ def test_reminder_rule_progresses_only_after_sent_deadline(tmp_path) -> None:
         level=1,
         name="Zahlungserinnerung",
         payment_deadline_days=14,
-        fee="0.00",
+        items=[],
     )
     findings = housekeeper.run(today=date(2026, 2, 10))
     reminder_task = next(item for item in findings if item.code == "reminder_due")
@@ -155,7 +157,7 @@ def test_reminder_levels_cannot_be_skipped(tmp_path) -> None:
             level=2,
             name="Erste Mahnung",
             payment_deadline_days=14,
-            fee="5.00",
+            items=[{"description": "Mahngebühr", "amount": "5.00"}],
         )
 
 
@@ -173,3 +175,106 @@ def test_payment_resolves_open_reminder_task(tmp_path) -> None:
 
     findings = housekeeper.run(today=date(2026, 2, 10))
     assert not any(item.code == "reminder_due" for item in findings)
+
+
+def test_reminder_can_carry_multiple_fee_items(tmp_path) -> None:
+    repository, member = _overdue_claim_repository(tmp_path)
+
+    draft = repository.create_reminder_draft(
+        member.member_id,
+        "claim-1",
+        level=1,
+        name="Rücklastschrift",
+        payment_deadline_days=14,
+        items=[
+            {"description": "Rücklastschriftgebühr", "amount": "5.00"},
+            {"description": "Bankgebühr", "amount": "3.50"},
+        ],
+    )
+    assert draft["fee_item_ids"] == []
+
+    sent = repository.mark_reminder_sent(member.member_id, "claim-1", draft["reminder_id"])
+    assert len(sent["fee_item_ids"]) == 2
+
+    data, claim = repository.get_claim(member.member_id, "claim-1")
+    descriptions = {item["description"] for item in claim["items"] if item["type"] == "fee"}
+    assert descriptions == {"Rücklastschriftgebühr", "Bankgebühr"}
+    assert claim_total(claim) == Decimal("108.50")
+
+
+def test_reminder_items_require_a_description(tmp_path) -> None:
+    repository, member = _overdue_claim_repository(tmp_path)
+
+    with pytest.raises(RepositoryError, match="Beschreibung"):
+        repository.create_reminder_draft(
+            member.member_id,
+            "claim-1",
+            level=1,
+            name="Rücklastschrift",
+            payment_deadline_days=14,
+            items=[{"description": "  ", "amount": "5.00"}],
+        )
+
+
+def test_reminder_with_zero_amount_items_creates_no_claim_item(tmp_path) -> None:
+    repository, member = _overdue_claim_repository(tmp_path)
+
+    draft = repository.create_reminder_draft(
+        member.member_id,
+        "claim-1",
+        level=1,
+        name="Zahlungserinnerung",
+        payment_deadline_days=14,
+        items=[{"description": "Mahngebühr", "amount": "0.00"}],
+    )
+    sent = repository.mark_reminder_sent(member.member_id, "claim-1", draft["reminder_id"])
+    assert sent["fee_item_ids"] == []
+    _data, claim = repository.get_claim(member.member_id, "claim-1")
+    assert claim_total(claim) == Decimal("100.00")
+
+
+def test_reminder_policy_round_trips_through_save_and_get(tmp_path) -> None:
+    repository = MemberRepository(tmp_path)
+    repository.initialize()
+
+    repository.save_reminder_policy(
+        grace_days_after_due=10,
+        levels=[
+            {"name": "Zahlungserinnerung", "fee": "0.00", "payment_deadline_days": 10},
+            {"name": "Mahnung", "fee": "7.50", "payment_deadline_days": 14},
+        ],
+        standard_fee_items=[
+            {"description": "Rücklastschriftgebühr", "default_amount": "6.00"},
+        ],
+    )
+
+    policy = repository.get_reminder_policy()
+    assert policy["grace_days_after_due"] == 10
+    assert [level["level"] for level in policy["levels"]] == [1, 2]
+    assert policy["levels"][1]["name"] == "Mahnung"
+    assert policy["levels"][1]["fee"] == "7.50"
+    assert policy["standard_fee_items"] == [
+        {"description": "Rücklastschriftgebühr", "default_amount": "6.00"}
+    ]
+
+
+def test_reminder_policy_rejects_invalid_input(tmp_path) -> None:
+    repository = MemberRepository(tmp_path)
+    repository.initialize()
+
+    with pytest.raises(RepositoryError, match="Mindestens eine Mahnstufe"):
+        repository.save_reminder_policy(grace_days_after_due=7, levels=[], standard_fee_items=[])
+
+    with pytest.raises(RepositoryError, match="benötigt einen Namen"):
+        repository.save_reminder_policy(
+            grace_days_after_due=7,
+            levels=[{"name": "  ", "fee": "0.00", "payment_deadline_days": 14}],
+            standard_fee_items=[],
+        )
+
+    with pytest.raises(RepositoryError, match="nicht negativ"):
+        repository.save_reminder_policy(
+            grace_days_after_due=7,
+            levels=[{"name": "Mahnung", "fee": "-1.00", "payment_deadline_days": 14}],
+            standard_fee_items=[],
+        )