feat(#1106): split bash mcp into hive-bash-daemon + hive-bash-mcp bridge

- new hive-bash-mcp crate: daemon (subprocess runner, wake signals) +
  stdio bridge (mcp tools). mirrors hive-matrix-mcp architecture
- hive-ag3nt: remove bash_runner.rs and bash_run/bash_status mcp tools;
  get_loose_ends uses hive_bash_mcp:🏃:active_tasks() via crate dep
- harness-base.nix: add hive-bash-daemon systemd service + auto-inject
  bash extraMcpServer into every agent (socket: /run/hive-bash/socket)

hive-ag3nt/src/bin/hive.rs

@@ -570,7 +570,6 @@ async fn serve_main<S: Surface>(socket: &Path, poll_ms: u64) -> Result<()> {
         S::send_to_parent(socket, failure).await;
     }
     tokio::spawn(hive_ag3nt::forge_notify::run(socket.to_path_buf()));
-    hive_ag3nt::bash_runner::spawn(socket.to_path_buf());
     // Log web_ui::serve's error instead of dropping it. A bare
     // `tokio::spawn(web_ui::serve(...))` discards the JoinHandle, so
     // any Err (e.g. EACCES from `bind_unix` when HIVE_WEB_SOCKET points