fix(windows): quote spaced paths in host agent Start-Process args

[patil2001]

Summary

Windows PowerShell 5.1 joins Start-Process -ArgumentList elements with spaces but no quoting, so any install path containing a space produced a truncated argv for the host agent (C:\Users\John instead of C:\Users\John Smith\...) and python exited instantly while the installer continued green. Agent args containing whitespace are now double-quoted before launch.

AI Assistance

AI-assisted review of generated task-script quoting. The author traced the argv split and is responsible for the final diff.

Release Lane

• Stable hotfix targeting release/2.6.x
• Mainline change targeting main
• Next-minor work targeting the next feature/minor release
• Not sure; reviewer should help classify

Stable hotfix reason:

Not targeting the stable release branch directly.

Changed Surface

• Docs only
• Tests only
• Dashboard UI
• Installer
• Core runtime
• Dashboard API
• CI workflows

Validation

• Diff reviewed against PS 5.1 Start-Process -ArgumentList joining semantics; PSScriptAnalyzer (lint-powershell.yml) will parse-check in CI (no local pwsh).