Create an Instance AI eval

Each eval is one JSON case. Author workflow cases in packages/@n8n/instance-ai/evaluations/data/workflows/. Author standalone Agent cases in packages/@n8n/instance-ai/evaluations/data/agents/ and follow the create-agent-builder-eval skill. The disk loader auto-discovers *.json in both directories. A LangTracer suite is the durable home. Cases validate against harness/schema.ts (.strict() — unknown keys fail at load). The eval README is the exhaustive field reference; this skill is the opinionated how.