Publish a draft as a new skill version

Compile the draft into ONE immutable version. The version is created exactly as the direct authoring routes create it: an owner or admin author's version is ready to enable immediately, and a version authored without that authority stays PROPOSED until an owner or admin approves it. Publishing does NOT enable the skill — enabling is a separate step with its own permission, so publishing from a draft is never a way around who may give a skill to the whole workspace.

A skill that has been published again by someone else since you started editing is refused until you review what changed (POST /skill-drafts/{id}/rebase).