Emergency stop: halt (or resume) this workspace's install of an authored skill

Break-glass for a skill of this workspace's own: set or clear the kill switch on whichever install the workspace holds of it, whoever took it. A killed instruction skill's guidance stops reaching prompts immediately, including its owner's.

This exists because a PERSONAL install is invisible to everyone but its owner, and so is its installation id, which left the per-install kill switch at PATCH /skill-installations/{id}/kill unreachable for exactly the untrusted prose it matters most for. Use that route whenever you can see the install; use this one when the workspace needs to stop a skill it cannot open. It answers 204 and nothing else: no installation id, no owner, no scope, no current state, so it restores the stop without disclosing anything the privacy fence protects. 404 only when this workspace has no install of the skill at all. Requires skills:edit.