Agent Skills: refactor:dotnet

Refactor ASP.NET Core/C# code to improve maintainability, readability, and adherence to best practices. Transforms fat controllers, duplicate code, and outdated patterns into clean, modern .NET code. Applies C# 12 features like primary constructors and collection expressions, SOLID principles, Clean Architecture patterns, and proper dependency injection. Identifies and fixes anti-patterns including service locator, captive dependencies, and missing async/await patterns.