Add central Javadoc platform for Grounds JVM APIs

[lusu007]

Context

Grounds JVM libraries now publish source and Dokka-backed Javadoc artifacts through gg.grounds.kotlin-conventions. We should expose those docs through one central public developer documentation surface instead of requiring developers to browse Maven artifacts or individual repository build outputs.

Goal

Create a central Javadoc/API documentation platform for Grounds JVM projects.

The platform should make it easy for plugin, service, and runtime developers to browse API docs for public Grounds libraries such as:

• library-jvm-modules
• grounds-minestom-runtime
• library-grpc-contracts
• public plugin/runtime libraries that publish JVM docs artifacts

Proposed Scope

• Decide where generated API docs should be hosted under the Grounds docs/developer documentation experience.
• Define how published Javadoc/Dokka artifacts are discovered or uploaded.
• Provide stable URLs per project and version.
• Make the latest stable version easy to find.
• Keep historical versions accessible when possible.
• Link the central API docs from the main documentation navigation.

Implementation Notes

Possible approaches:

• Publish generated Dokka/Javadoc output as static assets into the docs site during release workflows.
• Build a small docs index that links to per-project hosted Javadoc output.
• Use GitHub Pages, Cloudflare Pages, or the existing docs deployment target if it already supports static generated content.

The implementation should not require each library repo to hand-write API docs pages. Library repos should publish artifacts or generated docs; the docs platform should aggregate or link them.

Acceptance Criteria

• There is a public central entry point for Grounds JVM API documentation.
• At least one library, preferably library-jvm-modules, is wired end-to-end as the first example.
• The docs include project name, version, release date or source version, and a link to the repository.
• The process for adding another JVM library is documented.
• The page is linked from the public docs/developer navigation.