Migrate documentation to rdoc

[ydah]

Fixes: #5576

This PR completes the migration of the GraphQL Ruby documentation site from YARD/Jekyll to RDoc/Aliki.

It adds the RDoc build and CI checks, converts guide metadata and YARD comments, moves API-specific guide content into source comments, preserves legacy documentation URLs, and removes the legacy YARD pipeline. The generated API documentation is checked against the pre-migration public API inventory to detect unexpected coverage changes.

The generated site also includes GraphQL syntax highlighting, local-file-friendly image links, correct README rendering, nested guide navigation with page titles, and complete development guide table-of-contents links. No GraphQL runtime behavior is changed.

Validated with bundle exec rake docs:check, the documentation generator specs, the link checker, the RDoc reference checker, and the GraphQL highlighter tests.

[rmosolgo]

Hey, thanks so much for taking a crack at this! I just pulled the branch and built the docs locally. In general I think this is great, but I'd like to get a few more things before replacing the YARD docs with this:

• convert @api private to :nodoc:; right now they're rendered like this:

  

• Type deifnitions, somehow Prism has them in its RDoc: https://docs.ruby-lang.org/en/master/Prism/CallNode.html I would love to convert our YARD to types like that

I'm going to continue reviewing but I thought I'd share those ideas now to see what you think.

[ydah]

Thank you for the feedback! I've addressed both points:

• Converted @api private to :nodoc:
• Updated the type definitions so they're rendered properly in RDoc, similar to Prism

Thank you for catching these.

[rmosolgo]

Hey, thanks again for your work on this so far. I pulled the latest and took it for a spin today. I think a good approach would be to get this good enough and then continue iterating on master. Here are the things I think we need:

1. Ordered guides. This is currently implemented with index: ... in Jekyll frontmatter, but the new rendering puts them in alphabetical order. This means that Overview is no longer the first entry on the list, but it should be. I'm not sure how this should be implemented.

2. Call-outs for documented features which ship in GraphQL-Pro or GraphQL-Enterprise. This currently looks like this:

   

   But the new implementation doesn't include any indication that @defer isn't in GraphQL-Ruby OSS. I think this will be confusing and disappointing for people :S

   So we need something for that. A hard-coded indicator of some kind would work for me.

When those two are implemented, I'll be ready to merge this PR.

I think there will be a few things to address after that:

• Remove migration-related scripts that we don't need anymore
• Somehow improve local tooling to include file watching?
• The type annotation support is still not great :S I'm not sure what to do about that though. The way that you migrated YARD annotations seems like our best bet in RDoc because the inline-RBS notation doesn't support inline comments. (I really like how, in YARD, the argument name, type, and description all go together.)