fix: restore default fallbacks for client credentials in example

The test suite imports the example without env vars set. Removing the
fallback defaults caused ClientSecret to receive None, failing the
client_id validation.

Author: Larry-Osakwe

packages/mcp-fastmcp/examples/delegated_access/main.py

@@ -26,8 +26,8 @@
     # ClientSecret enables token exchange for delegated access
     application_credential=ClientSecret(
         (
-            os.getenv("KEYCARD_CLIENT_ID"),
-            os.getenv("KEYCARD_CLIENT_SECRET"),
+            os.getenv("KEYCARD_CLIENT_ID", "your-client-id"),
+            os.getenv("KEYCARD_CLIENT_SECRET", "your-client-secret"),
         )
     ),
 )