Enable GraphQL and phase11-demo examples; API improvements

Uncommented and enabled the 'examples/graphql-api' and 'examples/phase11-demo' in the workspace. Added missing dependencies and features to their Cargo.toml files. Improved API handler responses in both examples to use schema types for better OpenAPI/utoipa integration, and refactored guard logic in phase11-demo for more robust permission and role checks.

Author: Tuntii