Match both slash styles when removing build-machine paths from the
staged standalone bundle so the sanitization step works on Windows
and POSIX builds.
While touching the helper, replace the custom basename logic with
Node's built-in `path.basename` for clarity.
Prepare a dedicated `.next/electron-standalone` bundle before
running electron-builder so desktop packaging operates on a stable,
Electron-specific server payload.
This also adds a preflight that rejects standalone bundles whose
top-level `node_modules` is a symlink, because electron-builder
preserves `extraResources` symlinks and would otherwise ship an app
that depends on the build machine at runtime.
