✨ Updates API, C#, Docker, MSBuild, and Testing guidelines

Refines conventions for ASP.NET API endpoints, C# documentation,
Docker build arguments, MSBuild package management, and testing
method naming and structure. These changes aim to enhance clarity
and enforce best practices across the codebase.

.github/instructions/csharp.instructions.md

@@ -8,11 +8,10 @@ Code style is enforced by `.editorconfig`, `.globalconfig`, and StyleCop analyze
 
 ## Non-Obvious Defaults
 
-- XML doc comments required on public API in `src/` (suppressed in `tests/` and `samples/`).
+- XML doc comments required on all `public` and `protected` members in `src/` (suppressed in `tests/` and `samples/`).
 - Avoid `null!` (null-forgiving operator) — fix the nullability flow instead of suppressing the warning.
 
 ## Patterns
 
 - Prefer **records** for DTOs, value objects, and other immutable data carriers.
-- Use `LoggerMessage`-generated `partial` methods on a `partial class` — never log inline (e.g., `logger.LogInformation(…)`).
-
+- Use `LoggerMessage`-generated `partial` methods on a `partial class` — never log inline (e.g., `logger.LogInformation(…)`). If the containing type cannot be made `partial`, convert it to a `partial class` before adding logger methods. Do not fall back to inline logging.