Merged via consolidated batch validation. Fixes omniroute update on Windows (npm.cmd cannot be execFile'd without a shell on Node >=24, nodejs/node#52554). Extracts a shared bin/cli/npm-exec.mjs (also handles Bun, windowsHide) mirroring the existing server-side pattern in src/lib/services/installers/utils.ts. Own tests pass. Note: #11336 fixed the same underlying bug (#11335) with a narrower inline change; closed as duplicate crediting this more complete fix.
