✨ 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/msbuild.instructions.md

@@ -6,7 +6,9 @@ applyTo: "**/*.{csproj,props,targets}"
 
 ## Central Package Management
 
-All package versions are declared in `Directory.Packages.props` at the repo root. In `.csproj` files:
+All package versions are declared in `Directory.Packages.props` at the repo root. In `Directory.Packages.props`, ensure the last child element of the root `<Project>` tag is `<Import Project="Directory.Packages.template.props" />`. `Directory.Packages.template.props` is **READ ONLY**, never edit it. The template provides default `<PackageVersion>` entries; any entry with the same `Include` declared earlier in `Directory.Packages.props` takes precedence over the template default, because MSBuild uses first-definition-wins semantics and the import appears last.
+
+In `.csproj` files:
 
 ```xml
 <!-- Correct -->
@@ -22,6 +24,8 @@ To add or update a version, edit `Directory.Packages.props`:
 <PackageVersion Include="Newtonsoft.Json" Version="13.0.3" />
 ```
 
+If the package does not exist in the template, simply add a new `<PackageVersion>` entry in `Directory.Packages.props`. No override logic is needed; the entry will be the sole definition.
+
 ## Properties Set Centrally (Do Not Override)
 
 These are configured in the root `Directory.Build.props` — do **not** set them in individual projects:
@@ -37,3 +41,5 @@ Handled automatically via `<InternalsVisibleToSuffix>` in the root props. Defaul
   <InternalsVisibleTo Include="MyProject.IntegrationTests" />
 </ItemGroup>
 ```
+
+This is in addition to the automatically generated entries; do not remove or duplicate the default suffix entries.