Ship universal VSIX without bundled CLI binary

[MelbourneDeveloper]

TLDR;

Simplify the release pipeline to produce a single universal VSIX that no longer bundles the platform-specific CLI binary.

Details

• Remove the platform matrix (osx-arm64, osx-x64, linux-x64, win-x64) from the build-vsix job — now builds one universal VSIX
• Remove the .NET SDK setup and dotnet publish step from VSIX packaging
• Exclude the bin/ directory from the VSIX via .vscodeignore
• The separate build-cli job is unaffected and continues to produce platform-specific CLI artifacts

How do the tests prove the change works

Pipeline change — verified by successful CI build and VSIX packaging on push.