test: Update auth cookie tests to support theme preference

backend/tests/api/test_api_auth_cookie.py

@@ -13,7 +13,8 @@ def mock_user():
         id="user-123",
         username="test@example.com",
         display_name="Test User",
-        password_hash="hashed_password"
+        password_hash="hashed_password",
+        theme_preference="light"
     )
 
 def test_v1_prefix():
@@ -48,7 +49,7 @@ def test_register_sets_cookie():
     """Test that register sets the access_token cookie."""
     with patch("ea_chatbot.api.routers.auth.history_manager") as mock_hm:
         mock_hm.get_user.return_value = None
-        mock_hm.create_user.return_value = User(id="1", username="new@example.com", display_name="New")
+        mock_hm.create_user.return_value = User(id="1", username="new@example.com", display_name="New", theme_preference="light")
         
         response = client.post(
             "/api/v1/auth/register",
@@ -63,7 +64,7 @@ def test_auth_via_cookie():
     token = create_access_token(data={"sub": "123"})
     
     with patch("ea_chatbot.api.dependencies.history_manager") as mock_hm:
-        mock_hm.get_user_by_id.return_value = User(id="123", username="test@example.com", display_name="Test")
+        mock_hm.get_user_by_id.return_value = User(id="123", username="test@example.com", display_name="Test", theme_preference="light")
         
         # Pass token via cookie instead of header
         client.cookies.set("access_token", token)
@@ -93,7 +94,7 @@ def test_oidc_callback_redirects_with_cookie():
         }
         mock_oidc.exchange_code_for_token.return_value = {"id_token": "fake_id_token"}
         mock_oidc.validate_id_token.return_value = {"email": "sso@example.com", "name": "SSO User"}
-        mock_hm.sync_user_from_oidc.return_value = User(id="sso-123", username="sso@example.com", display_name="SSO User")
+        mock_hm.sync_user_from_oidc.return_value = User(id="sso-123", username="sso@example.com", display_name="SSO User", theme_preference="light")
         
         # Set the session cookie
         client.cookies.set("oidc_session", "fake_token")