dotnet-solid-principles Foundational design principles for .NET applications. Covers each SOLID principle with concrete C# anti-patterns and fixes, plus DRY guidance with nuance on when duplication is acceptable. These principles guide class design, interface contracts, and dependency management across all .NET project types. Scope boundary: This skill owns foundational SOLID/DRY design principles at the class and interface level. Architectural patterns (vertical slices, request pipelines, caching, idempotency) are owned by [skill:dotnet-architecture-patterns]. DI container mechanics (registr…