Verify the script installer and kcap update on real Windows #1483

The script installer (#1227) has only run on macOS and Linux; install.ps1 has only run under pwsh 7 on macOS. It needs a pass on a real Windows machine, under both Windows PowerShell 5.1 and pwsh 7.

Check on a clean Windows user account:

• irm https://<kcap-web>/install.ps1 | iex installs from the release manifest, verifies the checksum, and leaves kcap working in a new terminal (the user PATH is updated, nothing needs admin).
• The current junction points at the installed versions/<v> directory.
• The kcap refresh probe works, and the fallback path works when it is unavailable.
• A script-install kcap update (Update script installs in place and add kcap refresh #1340, in v1.2.2 and the 1.3 betas) switches current to the new version, including while a kcap process or the daemon holds the old binary open (locked-file path), and the daemon comes back on the new version.

Report anything that fails here or as a separate bug.