0.6.8: Windows Validation Restored

• Host PATH Resolution: resolveExecutableOnPath split PATH on :, so a Windows entry such as D:\tools was torn into two nonexistent directories and every host binary probe answered false. The lookup now splits on the platform delimiter.
• Portable Host Assertions: The host suite asserted an unescaped ExecStart= line and spawned /bin/echo, so Windows validation failed on a feature it correctly refuses to install there. Unit arguments are now verified by unquoting them back to the rendered path, the executable-bit case is scoped to platforms that have one, and the spawn probe runs the current Node binary.
• Changelog Sections Restored: The 0.6.1 and 0.6.5 headings were lost by later prepends, which left their records attributed to the following release. Both headings are restored with their original titles.