ci(windows): fix Build windows by locating vcvars64.bat via vswhere (windows-2025-vs2026)

[aflores-qb]

Problem

The build-windows-amd64 job in build_release.yml hardcodes the Visual Studio install path:

C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\Build\vcvars64.bat

GitHub is migrating the windows-latest runner image to windows-2025-vs2026 (runner notice: "windows-latest requests are being redirected to windows-2025-vs2026 by June 15, 2026"). The new image no longer has the 2022\Enterprise\ path, so the Build windows step fails instantly with:

The system cannot find the path specified.
##[error]Process completed with exit code 1.

This is environmental and breaks every PR plus develop itself — confirmed failing on develop (2026-06-13), #461 (2026-06-14), and #462 (2026-06-16), all at the same step.

Fix

Resolve the active Visual Studio installation dynamically with vswhere.exe (always present at the fixed Installer location) and call its vcvars64.bat. This is version/edition-agnostic and keeps the existing make-based build unchanged.

for /f "usebackq delims=" %%i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe" -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do set "VSINSTALL=%%i"
if not defined VSINSTALL ( echo Could not locate Visual Studio via vswhere & exit /b 1 )
call "%VSINSTALL%\VC\Auxiliary\Build\vcvars64.bat" && make build PLATFORM=windows SHELL_ENV=bash

microsoft/setup-msbuild was considered but is insufficient here: it only adds MSBuild to PATH and does not set up the cl.exe/C++ toolchain environment that the make build requires.

Impact

Unblocks the Windows build for all open PRs (#461, #462) and future ones. No code changes — CI workflow only.

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