Feuilles de poste : ajouter le référent en en-tête

Nom + téléphone du référent du poste (Position.lead_account_id), juste
sous le sous-titre (jour/lieu) — « Référent : à désigner » si aucun.
Même source que le référent affiché à l'écran bénévole
(volunteers.py:get_volunteer_planning).

Vérifié : pytest (287 passés, dont les nouveaux tests avec/sans
référent), ruff, alembic check — tous verts (pas de changement
frontend, la feuille reste un simple téléchargement de PDF).

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

backend/tests/test_position_sheets_api.py

@@ -50,6 +50,26 @@ def test_generates_a_pdf_with_assigned_volunteers(client, edition, session):
     assert resp.content.startswith(b"%PDF")
 
 
+def test_generates_a_pdf_with_a_referent(client, edition, session, make_account):
+    position = make_position(session, edition, name="Bar central")
+    make_shift(
+        session, edition, position, start=dt_at(9, 19), end=dt_at(9, 22),
+        min_staff=1, ideal_staff=2,
+    )
+    referent_volunteer = make_volunteer(session, edition, first_name="Sam", last_name="Nuit")
+    referent_account = make_account(
+        Role.LEAD, volunteer_id=referent_volunteer.id, email="referent@e.fr"
+    )
+    client.patch(
+        f"/editions/{edition.id}/positions/{position.id}",
+        json={"lead_account_id": str(referent_account.id)},
+    )
+
+    resp = client.post(_url(edition), json={})
+    assert resp.status_code == 200
+    assert resp.content.startswith(b"%PDF")
+
+
 def test_position_ids_filter_scopes_the_sheets(client, edition, session):
     bar = make_position(session, edition, name="Bar central")
     welcome = make_position(session, edition, name="Accueil")

backend/tests/test_position_sheets_pdf.py

@@ -68,3 +68,23 @@ def test_multiple_sheets_produce_a_larger_pdf():
     one = generate_position_sheets_pdf([_sheet()])
     two = generate_position_sheets_pdf([_sheet(), _sheet()])
     assert len(two) > len(one)
+
+
+def test_generates_a_valid_pdf_with_a_referent():
+    sheet = PositionDaySheet(
+        position_name="Bar central", position_location="Chapiteau",
+        date=dt.date(2026, 7, 10), shifts=(),
+        referent_name="Sam Nuit", referent_phone="0600000000",
+    )
+    pdf = generate_position_sheets_pdf([sheet])
+    assert pdf.startswith(b"%PDF")
+
+
+def test_generates_a_valid_pdf_without_a_referent():
+    sheet = PositionDaySheet(
+        position_name="Bar central", position_location="Chapiteau",
+        date=dt.date(2026, 7, 10), shifts=(),
+    )
+    assert sheet.referent_name is None
+    pdf = generate_position_sheets_pdf([sheet])
+    assert pdf.startswith(b"%PDF")