Add `!` prefix as a shorthand for `/shell` (e.g., `!ls -la`), with the
same admin permission checks. Also add optional `--timeout <seconds>`
parameter at the beginning of shell commands to override the default
60s timeout (e.g., `/shell --timeout 300 npm install`).
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>