fix: normalize paths consistently across platforms

- Fix completion.mts to return normalized targetPath with forward slashes
- Fix npm/paths.mts to remove WIN32 conditional that was converting
  forward slashes back to backslashes after normalization
- Remove unused WIN32 import from npm/paths.mts

The WIN32 conditional with path.normalize() was undoing the normalizePath()
call, causing tests to fail on Windows with backslashes instead of the
expected forward slashes.

Author: jdalton