Tell members which reference to put on a transfer

A data-review mail that lists the payment frequency but not how to pay leaves the
board matching anonymous transfers by hand. The mail now closes with the
reference to quote -- member number and full name, joined only where both exist
so a missing half cannot leave a dangling dash. Both are offered because either
identifies the payment on its own: a member who has forgotten their number falls
back on the name, and two members sharing a name are told apart by the number.

The note about the shortened IBAN moved out of the fixed template text into
{{data.iban_hint}}, filled only for members whose bank details are actually
listed -- it used to explain a masked IBAN to members who pay by transfer and see
no IBAN at all. It sits directly under the record as a parenthesised footnote,
which also keeps the dropped line from leaving a blank one behind.

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

tests/test_member_data_mail.py

@@ -4,11 +4,13 @@ from email.policy import default
 
 import pytest
 
+from ccma.domain.models import Member
 from ccma.services.member_data_mail import (
     data_review_recipients,
     generate_data_review_mails,
     mask_iban,
     member_data_fields,
+    payment_reference,
 )
 from ccma.storage.repository import MemberRepository, RepositoryError
 
@@ -75,6 +77,13 @@ def test_the_mail_lists_the_stored_record_of_that_member(tmp_path):
     assert "Telefon: 0621 123456" in content
     assert "PLZ und Ort: 68159 Mannheim" in content
     assert "Mitglied seit: 01.01.2026" in content
+    assert "Zahlweise: Halbjährlich" in content
+    # Both halves identify a transfer on their own, so both are offered.
+    assert "deine Mitgliedsnummer und/oder deinen vollen Namen" in content
+    assert f"{member.member_number} – Ada Lovelace" in content
+    # Nothing bank-related is stored, so the note about the shortened IBAN is left
+    # out instead of pointing at a line that is not there.
+    assert "verkürzt" not in content
     assert content.rstrip().endswith("Der Vorstand")
 
 
@@ -123,6 +132,23 @@ def test_bank_details_are_listed_with_a_masked_iban(tmp_path):
     assert "DE98670505050038907751" not in content
     assert "Mandatsreferenz: MANDAT-42" in content
     assert "Lastschriftmandat: aktiv, erteilt am 01.02.2026" in content
+    assert "(Die IBAN zeigen wir absichtlich nur verkürzt an" in content
+
+
+def test_the_transfer_reference_joins_number_and_name():
+    member = Member(
+        member_id="1", member_number="CCMA-0007", first_name="Ada", last_name="Lovelace"
+    )
+
+    assert payment_reference(member) == "CCMA-0007 – Ada Lovelace"
+    # The store insists on a member number, but a record read from elsewhere may not
+    # have one -- the name then carries the reference without a dangling dash.
+    assert (
+        payment_reference(
+            Member(member_id="1", member_number="", first_name="Ada", last_name="Lovelace")
+        )
+        == "Ada Lovelace"
+    )
 
 
 def test_mask_iban_keeps_country_and_last_four_digits():