drop the manager socket, the no-op migrate branch and other ruth special cases

start_manager bound the same path register_agent binds. The migrate branch, hive-priv-sock::MANAGER_NAME and MANAGER_CONTAINER were no-ops or dead. The send allow-list docs promised a manager exemption the code never had. Tests that used ruth as the manager fixture use plain names.

hive-c0re/src/main.rs

@@ -267,7 +267,6 @@ async fn cmd_serve(
     // Copy value first for the dashboard + knowledge-webhook tasks.
     let dashboard_port = env.dashboard_port;
     let coord = Arc::new(Coordinator::open(&db, env, model_prices, build_slots)?);
-    socket_server::start_manager(coord.clone())?;
     // Idempotent pre-flight: rewrite pre-meta-layout applied
     // repos, ensure proposed repos carry the `applied`
     // remote, bootstrap the meta repo, repoint containers at