Fix test result message parsing

[Daliys]

Summary

• Scope non-passing test result messages to NUnit failure, reason, or output nodes before falling back to result status.
• Add regression coverage for unrelated nested message nodes.
• Restore action-specific schema requirements for unity_scene_manager aliases.
• Add package-root AGENTS.md guidance and ignore local Gemini/Serena agent state.

Closes #106

Validation

• PYTHONDONTWRITEBYTECODE=1 scripts/prepush-validate.sh --static-only
• pre-push quick validation, including quick live server smoke