Improve contributor docs and test hygiene

[richardspink2]

Summary

• update contributor documentation links and local setup guidance for the current OpenCiv3 repo, .NET 8+, and Godot 4.4 .NET
• update vulnerable/outdated EngineTests package references, including the ImageSharp patched version
• add a shared test helper so Civ3 asset-dependent tests return early when local Civ3 data is unavailable

Why

The previous docs still referenced the old Prototype repository and older tooling. Local contributors without Civ3 installed could also hit asset-dependent test failures unless running under CI. This keeps the first-time contributor path cleaner without changing production behavior.

Validation

• dotnet restore C7/C7.sln --verbosity:minimal
• dotnet list C7/C7.sln package --vulnerable --include-transitive
• dotnet build C7/C7.sln --configuration Debug --verbosity:minimal
• dotnet format C7/C7.sln whitespace --verify-no-changes --verbosity minimal
• dotnet test C7/C7.sln --logger:'console;verbosity=minimal'
• git diff --check

Note: the rebased upstream branch currently emits existing compiler/analyzer warnings during build, but the build exits successfully and tests pass.

[richardspink2]

Here is a quick refresher of the docs and hygiene

[ajhalme]

Thanks for the contribution.

The documentation changes look reasonable. I would hold on to some of the comments that are being discarded here.

Pushing the test execution context logic into a helper is reasonable. A custom Civ3 test attribute could be a nice way to enable selective execution. Declaring the file dependencies at the test execution gate feels unnecessary.

[richardspink2]

Thanks for the review. I updated the branch to keep the Rider and CFC thread links, removed the explicit scenario file dependency lists from the test gates, and preserved the CI/local Civ3 context in the shared helper and scenario test.

Verified locally with:

• dotnet restore C7/C7.sln
• dotnet build C7/C7.sln
• dotnet format C7/C7.sln whitespace --verify-no-changes
• dotnet test C7/C7.sln
• git diff --check

[ajhalme]

Thanks. Looks fine to me.