test: Resolve DeprecationWarnings in theme tests by using client.cookies.set

backend/tests/api/test_theme.py

@@ -25,10 +25,8 @@ def test_get_me_includes_theme(test_user, auth_token):
     with patch("ea_chatbot.api.dependencies.history_manager") as mock_hm:
         mock_hm.get_user_by_id.return_value = test_user
         
-        response = client.get(
-            "/api/v1/auth/me",
-            cookies={"access_token": auth_token}
-        )
+        client.cookies.set("access_token", auth_token)
+        response = client.get("/api/v1/auth/me")
         
         assert response.status_code == 200
         data = response.json()
@@ -53,10 +51,10 @@ def test_update_theme_success(test_user, auth_token):
         # The router uses its own reference to history_manager
         mock_hm_router.update_user_theme.return_value = updated_user
         
+        client.cookies.set("access_token", auth_token)
         response = client.patch(
             "/api/v1/auth/theme",
-            json={"theme": "dark"},
-            cookies={"access_token": auth_token}
+            json={"theme": "dark"}
         )
         
         assert response.status_code == 200