Agent Skills: csharp-file-based-apps

Write and run C# programs without a .csproj or solution file using .NET 10+ file-based apps, including multi-file apps with `#:include` (.NET 11+). Use when the user wants to execute C# code quickly — scripts, utilities, prototyping, quick experiments, data processing, teaching examples, or tool authoring. Triggers on phrases like "run this C# file", "C# script", "no project file needed", "single file C# app", "dotnet run file.cs", "quick C# utility", "split script across files", "#:include directive", or any request to write and immediately execute a small self-contained C# program.