Fixes#1469.
On Windows the `claude` binary installed via `npm i -g @anthropic-ai/claude-code`
is `claude.cmd`, and Node's spawn() cannot resolve .cmd wrappers via PATH
without shell: true. The call failed with `spawn claude ENOENT` and claw.js
returned an error string to the caller.
Mirrors the fix pattern applied in PR #1456 for the MCP health-check hook.
'claude' is a hardcoded literal (not user input), so enabling shell on Windows
only is safe.