docs(tools/bash): document mcp__bash__kill tool

feat b16629801b added the kill tool to
hive-bash-mcp but docs/tools/bash.md wasn't updated. The tool was
described only in the MCP server tool-description string; add a proper
section to the reference doc.

kill(id, force?) fires SIGINT (force: false, default) or SIGKILL
(force: true) to the task's process group. Fire-and-forget — the
completion wake fires as usual. A pending task is cancelled outright.
Escalation pattern: SIGINT first, then force: true if it doesn't exit.

docs/tools/bash.md

@@ -56,6 +56,24 @@ silently blocked.
 
 Exposed as `mcp__bash__status`.
 
+### `kill(id, force?)`
+
+Stop a running or pending task by its ID (from `run`). Fire-and-forget:
+sends the signal and returns without waiting — handle the completion
+wake (`from: "bash-task-<id>"`) on a future turn.
+
+- `force: false` (default) — SIGINT to the task's **process group**
+  (graceful; lets the process clean up). The whole process group is
+  signalled, so children spawned by the shell (cargo, nix, etc.) are
+  also stopped.
+- `force: true` — SIGKILL.
+
+If a SIGINT'd task doesn't exit, call `kill` again with `force: true`.
+A still-pending task is cancelled before it starts. The task ends as
+`killed` and fires the usual completion wake.
+
+Exposed as `mcp__bash__kill`.
+
 ## Namespace note
 
 `run` and `status` live in the `bash` MCP server, not `hyperhive`. So