* replace the `YEAR` tab with `OVERVIEW` tab, which will analyze most recent 20K commits
* use `LiveChartsCore.SkiaSharpView.Avalonia` instead of a custom chart view
* remove dotnet-tool.json because the project does not rely on any dotnet tools.
* remove Directory.Build.props because the solution has only one project.
* move src/SourceGit to src. It's not needed to put all sources into a subfolder of src since there's only one project.