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-bash-mcp/src/lib.rs

@@ -0,0 +1,10 @@
+//! Shared library for `hive-bash-daemon` and `hive-bash-mcp`.
+//!
+//! The daemon owns the subprocess runner loop and unix socket server.
+//! The stdio MCP bridge is a thin client that forwards each tool call
+//! to the daemon over the unix socket.
+
+pub mod paths;
+pub mod protocol;
+pub mod runner;
+pub mod socket;