Get workflow definition — Arazzo spec and input schema

Returns the workflow definition with content negotiation:

• application/json (default): workflow metadata with simplified step info
• application/vnd.oai.workflows+json: raw Arazzo document as JSON
• application/vnd.oai.workflows+yaml: raw Arazzo document as YAML
• text/markdown: compact LLM-friendly summary with input schema and steps
• text/html: human-readable HTML summary Execute via broker: POST /{jentic_host}/workflows/{slug}