Support DISM in host initialization with MSIX PowerShell - #98

Summary

• Import the DISM module through Windows PowerShell compatibility when host_init.ps1 runs in MSIX-packaged PowerShell 7, retaining native DISM calls for unpackaged installs.
• Stop on DISM query or installation errors instead of continuing with setup after a failed feature check.
• Document the workaround and the separate PowerShell 7 remoting limitation of MSIX for the rest of the lab.

Workaround for PowerShell/PowerShell#13866.

Validation

• PowerShell syntax parsed successfully, and the compatibility import exposed all four DISM commands as proxy functions locally.
• User reports running the updated script on their machine; the host's feature state was not independently verified in this worktree.