Get Workflow Markdown

Render this workflow as a markdown document. For showing a person what a workflow is: the pipeline in execution order with parallel steps as branches, retry loops called out on their own line, a node table with each node's configuration, the voices, and the quality gates with what each one does on failure. Text only, and printable as-is on any surface including a terminal: there is no diagram, because the pipeline section already states the graph, retry loops included. The rendering is server-side so every client describes a graph the same way. A renderer in each CLI and each UI would diverge the first time a node type shipped, and nothing would report the divergence. `definition` is config-migrated first, exactly as `GET /workflows/{id}` returns it, so the document never describes a node config the API no longer serves.