dotfiles: Windows dev-box provisioning scripts

dotfiles: Windows dev-box provisioning scripts

Extracted from a native Windows project so the box setup can be reused
and versioned on its own.

setup-windows.bat runs the non-elevated half (winget installs, user PATH
edits for WinMerge and BinSkim, global git config) and then launches
setup-windows-with-uac.ps1 elevated, printing its transcript when the
elevated window closes.

setup-windows-with-uac.ps1 enables ssh-agent and installs Visual Studio
2022 Community in three labelled passes (base C++ workload, Clang/LLVM,
v141 + Windows XP toolset), the WDK 10.0.26100, and the Windows
Performance Toolkit.

The global git identity is PLACEHOLDER_NAME / PLACEHOLDER_EMAIL and must
be edited before the script is run. The runtime transcript
(setup-windows-uac.log) is gitignored: it embeds local machine paths.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>