Allocate open claims and donations directly from the payment dialog

Recording a payment previously meant saving it bare, then separately
opening a claim to allocate money to it. Zahlung anlegen now lists a
member's open claims and donations right in the same dialog with a
select + amount field to assign parts of the payment on the spot, and a
"Neue Spende anlegen" button to create a donation inline and allocate to
it immediately -- covering members who pay more than the membership fee
in one transfer.

Shared the same allocation table in the existing payment-edit dialog so
editing a payment shows and preserves donation allocations too; before
this, saving an edited payment silently dropped any donation allocation
because update_payment only round-tripped claim allocations.

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

tests/test_contributions.py

@@ -441,6 +441,101 @@ def test_existing_free_payment_can_be_allocated_to_a_donation(tmp_path) -> None:
         )
 
 
+def test_payment_can_be_created_with_immediate_claim_and_donation_allocation(tmp_path) -> None:
+    repository, member = _repository_with_claim(tmp_path, amount="30.00")
+    donation = repository.record_donation(
+        member.member_id, donation_date="2026-06-21", amount="20.00", reference="Aufrundung"
+    )
+
+    payment = repository.create_payment(
+        member.member_id,
+        payment_date="2026-06-21",
+        amount="50.00",
+        claim_allocations={"claim-1": "30.00"},
+        donation_allocations={donation["donation_id"]: "20.00"},
+        reference="Mitgliedsbeitrag plus Spende",
+    )
+
+    data = repository.get_contributions(member.member_id)
+    _data, claim = repository.get_claim(member.member_id, "claim-1")
+    assert claim_balance(data, claim) == Decimal("0.00")
+    assert donation_balance(data, donation) == Decimal("0.00")
+    assert payment_allocated_total(data, payment["payment_id"]) == Decimal("50.00")
+
+
+def test_payment_creation_rejects_allocations_exceeding_amount(tmp_path) -> None:
+    repository, member = _repository_with_claim(tmp_path, amount="30.00")
+
+    with pytest.raises(RepositoryError, match="übersteigen den"):
+        repository.create_payment(
+            member.member_id,
+            payment_date="2026-06-21",
+            amount="10.00",
+            claim_allocations={"claim-1": "30.00"},
+        )
+
+
+def test_updating_payment_without_donation_allocations_preserves_existing_ones(tmp_path) -> None:
+    repository = MemberRepository(tmp_path)
+    repository.initialize()
+    member = repository.create_member(first_name="Donation", last_name="Preserve")
+    donation = repository.record_donation(
+        member.member_id, donation_date="2026-06-21", amount="20.00", reference="Sommerfest"
+    )
+    payment = repository.record_donation_payment(
+        member.member_id,
+        donation["donation_id"],
+        payment_date="2026-06-21",
+        amount="20.00",
+        allocation_amount="20.00",
+    )
+
+    repository.update_payment(
+        member.member_id,
+        payment["payment_id"],
+        payment_date="22.06.2026",
+        amount="20.00",
+        allocations={},
+        reference="Korrigierte Referenz",
+    )
+
+    data = repository.get_contributions(member.member_id)
+    assert donation_allocated_total(data, donation["donation_id"]) == Decimal("20.00")
+    assert data.payments[0]["reference"] == "Korrigierte Referenz"
+
+
+def test_updating_payment_with_donation_allocations_replaces_them(tmp_path) -> None:
+    repository = MemberRepository(tmp_path)
+    repository.initialize()
+    member = repository.create_member(first_name="Donation", last_name="Replace")
+    first_donation = repository.record_donation(
+        member.member_id, donation_date="2026-06-21", amount="20.00", reference="Erste Spende"
+    )
+    second_donation = repository.record_donation(
+        member.member_id, donation_date="2026-06-21", amount="20.00", reference="Zweite Spende"
+    )
+    payment = repository.record_donation_payment(
+        member.member_id,
+        first_donation["donation_id"],
+        payment_date="2026-06-21",
+        amount="20.00",
+        allocation_amount="20.00",
+    )
+
+    repository.update_payment(
+        member.member_id,
+        payment["payment_id"],
+        payment_date="2026-06-21",
+        amount="20.00",
+        allocations={},
+        donation_allocations={second_donation["donation_id"]: "20.00"},
+    )
+
+    data = repository.get_contributions(member.member_id)
+    assert donation_allocated_total(data, first_donation["donation_id"]) == Decimal("0.00")
+    assert donation_allocated_total(data, second_donation["donation_id"]) == Decimal("20.00")
+
+
 def test_gnucash_id_is_unique_across_member_store(tmp_path) -> None:
     repository, first_member = _repository_with_claim(tmp_path / "store")
     repository.record_payment(