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/app/services/test_crud_service.py

@@ -70,7 +70,10 @@ def _build_test_query(
     Kept as a single source of truth so the displayed page of results and
     the total count it's paginated against can never drift apart.
     """
-    query = db.query(Test).options(joinedload(Test.technique))
+    query = db.query(Test).options(
+        joinedload(Test.technique),
+        joinedload(Test.red_tech_assigned_user), joinedload(Test.blue_tech_assigned_user),
+    )
 
     # Check: state
     if state: