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/main.rs

@@ -0,0 +1,32 @@
+//! `hive-bash-daemon` binary — long-running per-agent bash task runner.
+//! Spawns `sh -c` subprocesses, monitors completion, writes task state
+//! files, and fires hyperhive wake signals. Listens on a unix socket
+//! for tool-call requests from the `hive-bash-mcp` stdio bridge.
+
+use anyhow::Result;
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    tracing_subscriber::fmt()
+        .with_env_filter(
+            tracing_subscriber::EnvFilter::try_from_env("RUST_LOG")
+                .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info")),
+        )
+        .init();
+
+    let socket_path = hive_bash_mcp::paths::daemon_socket();
+    let wake_socket = hive_bash_mcp::paths::hyperhive_socket();
+
+    tracing::info!(
+        socket = %socket_path.display(),
+        wake = %wake_socket.display(),
+        "hive-bash-daemon starting"
+    );
+
+    // Start the background runner loop — scans for pending tasks and
+    // spawns them, sends wake signals on completion.
+    hive_bash_mcp::runner::spawn_loop(wake_socket);
+
+    // Serve the unix socket forever.
+    hive_bash_mcp::socket::serve(&socket_path).await
+}