fix(distribution): align Windows installer with R2

[Teakowa]

Summary

• make install.ps1 use https://releases.wrightkit.dev by default instead of GitHub Release/API URLs
• resolve latest Windows installs through latest/version and download from latest/, while pinned installs use immutable releases/<version>/ paths
• update the Windows installer fixture to model the R2 contract while preserving missing-version, checksum-failure, and native smoke coverage
• remove the versioned fixture before the latest-install check so that test fails if latest silently falls back to the versioned path

Verification

• reviewed the branch diff against main
• verified install.ps1 no longer contains a default GitHub Release/API dependency
• ablation: the latest-path test removes releases/<version> before installation, so the case only passes when /latest/version + /latest/<artifact> are actually used
• Windows execution is left to the repository's existing distribution CI leg

Fixes #284