Replace bare `node gsd-tools.cjs` invocations with `node "\$GSD_TOOLS"` throughout
the CLI Usage section, and add a comment explaining that \$GSD_TOOLS resolves to the
full installed bin path (global or local). Bare relative paths only work from the
install directory and silently fail when run from a project root.
Closes#2245
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>