Enable Windows releases without Windows CI/CD dependency

[Copilot]

Windows releases required windows-latest runners and 25-minute builds. This changes to a pre-built executable approach: build once on Windows, commit to repo, package from Linux.

Changes

Workflow simplification

• build-windows job now runs on ubuntu-latest
• Removed Visual Studio setup, library downloads, MSBuild compilation
• Checks for pre-built BeamCommander.exe in bin/, packages with zip
• Workflow time: 25min → 30sec

Files removed

• Visual Studio project files (.sln, .vcxproj, .vcxproj.filters)
• Icon resources (icon.rc, *.ico)
• Windows-specific build documentation

Documentation added

• .github/BUILD_WINDOWS_EXECUTABLE.md - Instructions for building on Windows with Visual Studio or MSYS2/MinGW
• Updated .github/WINDOWS_BUILD.md - Describes one-time build workflow

Usage

Build executable once on Windows, commit to openframeworks-src-master/apps/myApps/BeamCommander/bin/:

# On Windows: build BeamCommander.exe
git add openframeworks-src-master/apps/myApps/BeamCommander/bin/BeamCommander.exe
git commit -m "Add pre-built Windows executable"
git push

Create releases from any machine:

git tag v1.0-windows
git push origin v1.0-windows

Workflow packages pre-built executable with documentation, creates release. No Windows runners required after initial build.

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