refactor(job-controller): drop the subagent ownership fence from job.kill

The registry's owner fence is the only access rule for a human kill: a job
is killable by the session whose list carries it, and a child session's own
jobs are no exception. The fence had pulled two implementation helpers out
of the Session Controller's package entry (plus a safe-host-export exception
for them) so the job controller could import them; both go, and the job
controller no longer depends on the agent registry or the Session Controller.

scripts/package-dependency-policy.ts

@@ -45,7 +45,6 @@ const DUPLICATE_SAFE_PACKAGES: readonly string[] = [
  * prominent heading in the pull request description.
  */
 const SAFE_HOST_DEPENDENCY_EXPORTS = {
-  '@deepseek-ai/dsh-api-session-controller': ['apiSessionSubagentOwnershipError', 'hasApiSessionSubagentOwner'],
   '@deepseek-ai/dsh-credentials': ['credentialKey'],
   '@deepseek-ai/dsh-deque': ['Deque'],
   '@deepseek-ai/dsh-llm': ['callConfigEquals'],