Adds it to `DEPRECATED_BUILTIN_WORKFLOW_IDS` — the registry's own retirement
mechanism, and the reason `isBuiltinWorkflowToggleEligible` and
`validateEnabledBuiltinWorkflowIds` exist. The workflow disappears from new
selection while `getBuiltinWorkflow` keeps resolving it, so any task that already
selected it still runs. Built-ins cannot be deleted, and deleting this one would
strand those tasks.
It is obsolete because builtin:coding-ideas-v2 supersedes it and because its own
success path could never complete: `code-review -> documentation-delivery` puts a
write-capable node after a passed review, which the graph refuses with
`workspace-review-seal-required`.
d061081b61