- add static 'role' (authority|follower) to NodeConfig/CastleConfig, wired from
castle.yaml through the registry to the mesh wire; civil pinned authority
- castle-presence: TTL KV bucket each node renews (churn signal); delete-on-stop
- castle-config: authority-gated get/put + change-watch SSE (follower reconcile
hook hangs off it)
- bound the NATS drain on stop() so shutdown can't hang
- tests: role config/registry round-trip, wire round-trip, role write-gating
Single-node verified; follower reconcile pending the second node.