Feat: Categories & indexing of code

[Codeshark-NET]

https://www.mediawiki.org/wiki/Help:Categories as an example.

This will enable us add tags in the code repo docs and let DocSearch index it. This would be usable for tagging code related to bases (like all Nitrox patches that patch base code) and our abstraction over bases, etc.

More info: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/documentation-comments#d33-code

Suggested by @Measurity