On Windows, os.Symlink requires Developer Mode or admin privileges.
Extract symlink creation into platform-specific files: on non-Windows,
behavior is unchanged (os.Symlink). On Windows, try os.Symlink first,
then fall back to directory junctions (mklink /J) for dirs and file
copy for files.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>