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>

src/ccma/services/member_data_mail.py

@@ -38,6 +38,15 @@ DEFAULT_RECIPIENT_STATUSES: tuple[str, ...] = (
 # empty line the eye skips over.
 NOT_STORED = "(nicht hinterlegt)"
 
+# Only makes sense next to a masked IBAN, so it is filled per member rather than
+# written into the template as a fixed line. It sits directly under the record and
+# reads as a footnote to it, which is also why it carries its own parentheses: a
+# dropped line must not leave a blank one behind.
+IBAN_HINT = (
+    "(Die IBAN zeigen wir absichtlich nur verkürzt an – die letzten vier Stellen "
+    "genügen zum Abgleich.)"
+)
+
 
 @dataclass(frozen=True, slots=True)
 class GeneratedDataReviewMail:
@@ -106,9 +115,7 @@ def member_data_fields(member: Member) -> list[tuple[str, str]]:
             ),
         ]
     )
-    if any(
-        value.strip() for value in (member.iban, member.mandate_reference, member.account_holder)
-    ):
+    if has_bank_details(member):
         signed = format_date_for_display(member.mandate_signed_at)
         fields.extend(
             [
@@ -125,6 +132,30 @@ def member_data_fields(member: Member) -> list[tuple[str, str]]:
     return [(label, value.strip() or NOT_STORED) for label, value in fields]
 
 
+def has_bank_details(member: Member) -> bool:
+    """Whether the club stores anything about this member's account at all. Members
+    who pay by transfer have nothing here, and asking them to check a mandate they
+    never gave is noise."""
+    return any(
+        value.strip() for value in (member.iban, member.mandate_reference, member.account_holder)
+    )
+
+
+def payment_reference(member: Member) -> str:
+    """What the member should write on a transfer. Both halves are offered because
+    either one identifies the payment on its own: a member who has forgotten their
+    number can fall back on the name, and a name shared by two members is told apart
+    by the number."""
+    return " – ".join(
+        part
+        for part in (
+            member.member_number.strip(),
+            " ".join(value for value in (member.first_name, member.last_name) if value).strip(),
+        )
+        if part
+    )
+
+
 def data_review_recipients(
     repository: MemberRepository, *, statuses: tuple[str, ...] | None = None
 ) -> list[Member]:
@@ -156,6 +187,8 @@ def data_review_mail_bytes(
             "member.iban_masked": mask_iban(member.iban),
             "data.sheet": "\n".join(f"{label}: {value}" for label, value in fields),
             "data.count": str(len(fields)),
+            "data.iban_hint": IBAN_HINT if has_bank_details(member) else "",
+            "payment.reference": payment_reference(member),
         }
     )
     rendered = render_template(repository, "data_review", values, {"data": entries})