fix(ci): restore prebuilt Z3 on Windows

[prekshivyas]

Summary

Restore the Windows MSVC tasks to the official architecture-matched prebuilt Z3 4.16.0 static libraries selected in #2738. This reverses the source-build fallback introduced in #3163 now that authenticated GitHub release lookup is restored.

Related Issue

No issue required: localized Windows CI regression following #2738 and #3163.

Changes

• Enable the prebuilt-z3 feature for Windows checks, tests, lint, and release builds.
• Pin Z3_SYS_Z3_VERSION=4.16.0.
• Pass the read-only GitHub workflow token to avoid unauthenticated API throttling.
• Restore prebuilt Z3 guidance for native and cross-compiled Windows builds.

Testing

• PowerShell parser accepts tasks/scripts/windows-msvc.ps1.
• git diff --check.
• Verified z3-sys 0.11.0 consumes Z3_SYS_Z3_VERSION and READ_ONLY_GITHUB_TOKEN.
• cargo check -p openshell-prover --features prebuilt-z3: blocked locally because this ARM64 host lacks the Clang compiler required by ring; CI provides the documented Visual Studio Clang component.
• mise run pre-commit: mise is unavailable in this shell.

Checklist

• Follows Conventional Commits.
• Commit is signed off (DCO).
• Architecture and contributor documentation updated.