#1152 fix: Windows CLI install no longer fails during binary verification

Summary

• Windows CLI install and update now avoid a staged executable name that Windows can treat as an installer.
• Added focused installer harness coverage so the PowerShell installer keeps using a neutral staged executable name.

User Impact

• Before, Windows CLI install could fail with uloop binary verification failed when the staged executable triggered Windows installer elevation behavior.
• After, binary verification runs under a neutral staged filename, so the install can complete without an unexpected admin prompt.

Changes

• Rename the PowerShell installer temporary directory prefix to uloop-stage-.
• Rename the staged executable prefix from uloop-install- to uloop-staged-.
• Add a regression check to the installer release-filter harness.

Verification

• bash scripts/test-install-release-filter.sh
• Windows PowerShell parse check for scripts/install.ps1
• pwsh parse check for scripts/install.ps1
• Local latest-beta PowerShell install smoke test
• codex review --base origin/v3-beta