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)

Cargo.lock

@@ -1226,6 +1226,7 @@ dependencies = [
  "axum",
  "clap",
  "futures-util",
+ "hive-bash-mcp",
  "hive-sh4re",
  "reqwest",
  "rmcp",
@@ -1241,6 +1242,21 @@ dependencies = [
  "tracing-subscriber",
 ]
 
+[[package]]
+name = "hive-bash-mcp"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "hive-sh4re",
+ "rmcp",
+ "schemars",
+ "serde",
+ "serde_json",
+ "tokio",
+ "tracing",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "hive-c0re"
 version = "0.1.0"