feat(tests): add team queue overview section for leads

red_lead/blue_lead never saw a plain "All Tests" list — they were always
routed into their own review two-queue view or "My Tasks", with no way to
see every test and who's actually working it. Adds an always-visible
section at the end of the Tests page for leads showing every test with
both Red and Blue assignee columns, so they can monitor the queues and
spot a stuck ticket or an overloaded operator.

The list endpoint (GET /tests) now joinedloads the assignee relationships
and resolves usernames the same way the detail endpoint already does, so
the new section doesn't depend on GET /users/operators (lead/manager-only).

backend/tests/test_test_assignee_username.py

@@ -61,3 +61,24 @@ def test_assignee_username_is_none_when_unassigned(client, db, red_lead_headers,
     body = resp.json()
     assert body["red_tech_assignee"] is None
     assert body["red_tech_assignee_username"] is None
+
+
+def test_list_endpoint_resolves_assignee_usernames_for_team_queue_overview(
+    client, db, red_lead_headers, red_lead_user, red_tech_user, blue_tech_user,
+):
+    """The leads' 'All Tests — Team Queue Overview' section reads assignee
+    usernames off GET /tests (the list endpoint), not just the detail
+    endpoint — both must resolve them the same way."""
+    technique = _seed_technique(db)
+    _seed_test(
+        db, technique, red_lead_user.id,
+        red_tech_assignee=red_tech_user.id, blue_tech_assignee=blue_tech_user.id,
+    )
+
+    resp = client.get("/api/v1/tests", headers=red_lead_headers)
+
+    assert resp.status_code == 200, resp.text
+    body = resp.json()
+    match = next(t for t in body if t["red_tech_assignee"] == str(red_tech_user.id))
+    assert match["red_tech_assignee_username"] == red_tech_user.username
+    assert match["blue_tech_assignee_username"] == blue_tech_user.username