Fix test utility runtime schema: add missing isNode field to NodeSpec interface and objects

- Add isNode: boolean field to NodeSpec interface in test utility file
- Add isNode: true to all NodeSpec objects to match corrected interface structure
- Resolves TypeScript compilation error in CI meta tests
- Meta tests now pass locally with updated schema structure

Co-Authored-By: Dan Lynch <pyramation@gmail.com>

Author: devin-ai-integration[bot]