Adds GET/PUT/DELETE /api/hosts/{id}/admin-credentials handlers that
mirror the existing repo-credentials endpoints but write to
store.CredKindAdmin with AEAD additional-data "host:<id>:admin" (scoped
away from the repo slot to prevent cross-binding). PUT immediately pushes
a config.update(Slot:"admin") to the agent when it is connected, and the
new pushAdminCredsToAgent helper is wired for use by the upcoming prune
run-now endpoint (D2) to push on-demand before dispatch.
steve
e7960151fb