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/Cargo.toml

@@ -0,0 +1,35 @@
+[package]
+name = "hive-bash-mcp"
+edition.workspace = true
+version.workspace = true
+
+[lints]
+workspace = true
+
+[dependencies]
+anyhow.workspace = true
+hive-sh4re.workspace = true
+rmcp.workspace = true
+schemars.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+tokio.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+
+# `hive-bash-daemon` — long-running per-agent bash task runner.
+# Spawns `sh -c` subprocesses, monitors completion, writes task state
+# files under harness/bash-tasks/, and fires hyperhive wake signals on
+# completion. Listens on a unix socket for tool-call requests from the
+# stdio MCP bridge.
+[[bin]]
+name = "hive-bash-daemon"
+path = "src/main.rs"
+
+# `hive-bash-mcp` — thin stdio MCP bridge spawned by claude per turn.
+# Forwards every tool call (bash_run, bash_status) to the daemon over
+# the unix socket, returns results to claude. No subprocess management
+# at this entrypoint — the daemon owns that.
+[[bin]]
+name = "hive-bash-mcp"
+path = "src/bin/mcp.rs"