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/lib.rs

@@ -1,7 +1,6 @@
 //! Shared in-container harness code used by both `hive-ag3nt` (agent) and
 //! `hive-m1nd` (manager) binaries.
 
-pub mod bash_runner;
 pub mod client;
 pub mod events;
 pub mod forge_notify;