Add CI workflow

[perust]

Summary

• Add a basic GitHub Actions CI workflow for this repository.
• The workflow runs the same lightweight checks used during the repo health sweep: syntax checks, compile checks, tests, build, or platform-specific build/test depending on the project type.

Verification

• Ran the closest local equivalent of the workflow before opening this PR.
• For Windows/WPF workflow, local Linux verification is not possible; the workflow uses windows-latest and .NET 8.