Badges : ordre de superposition des champs

La photo recouvrait le nom et le texte libre (champs dessinés dans l'ordre
alphabétique de leur type). BadgeField.z_order (migration 0028, champs
existants renumérotés photo dessous) fixe l'ordre de dessin du PDF et de
l'aperçu ; boutons « Premier plan / Avancer / Reculer / Arrière-plan »
dans l'inspecteur.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/tests/test_badges_api.py

@@ -398,3 +398,41 @@ def test_badge_count_out_of_range_is_rejected(client, edition, session, count):
         f"/editions/{edition.id}/volunteers/{volunteer.id}", json={"badge_count": count}
     )
     assert resp.status_code == 422
+
+
+def test_fields_are_drawn_in_stacking_order(client, edition, session, monkeypatch):
+    import app.api.badges as badges_api
+
+    captured = {}
+    original = badges_api.generate_badge_sheets_pdf
+
+    def spy(badges, *args, **kwargs):
+        captured["badges"] = badges
+        return original(badges, *args, **kwargs)
+
+    monkeypatch.setattr(badges_api, "generate_badge_sheets_pdf", spy)
+    resp = client.put(
+        f"{_badges_url(edition)}/template/fields",
+        json={
+            "fields": [
+                _field(field_type="FREE_TEXT", text="Staff", z_order=2),
+                _field(field_type="FULL_NAME", z_order=0),
+                _field(field_type="PHOTO", z_order=1),
+            ]
+        },
+    )
+    assert resp.status_code == 200
+    assert [f["field_type"] for f in resp.json()] == ["FULL_NAME", "PHOTO", "FREE_TEXT"]
+    make_volunteer(session, edition, first_name="Alex", last_name="Martin")
+
+    assert client.post(f"{_badges_url(edition)}/generate", json={}).status_code == 200
+    (badge,) = captured["badges"]
+    assert [f.text for f in badge.fields] == ["Alex\nMartin", "AM", "Staff"]
+
+
+def test_photo_is_drawn_below_text_at_equal_stacking_order(client, edition):
+    resp = client.put(
+        f"{_badges_url(edition)}/template/fields",
+        json={"fields": [_field(field_type="FULL_NAME"), _field(field_type="PHOTO")]},
+    )
+    assert [f["field_type"] for f in resp.json()] == ["PHOTO", "FULL_NAME"]