Add CI pipeline with GitHub Actions

No CI pipeline exists. Set up a GitHub Actions workflow that: builds the solution (dotnet build), runs all tests (dotnet test), and reports results. Trigger on push to main and on pull requests. Use .NET 10 SDK.

Start by inspecting the solution and test projects, then run dotnet build and dotnet test locally with the .NET 10 SDK. Set up a GitHub Actions workflow triggered by pushes to main and pull requests; done means the workflow builds the solution, runs all tests, and reports their results.

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