docs: Publish rustdoc for internal crates alongside mdbook

[cgwalters]

The docs workflow now also generates rustdoc for all workspace crates and publishes them as a subdirectory of the main documentation site. This makes internal API documentation available at bootc-dev.github.io/bootc/internals.html with links to each crate.

Changes:

• Switch docs container to CentOS Stream 10 for newer Rust (1.91)
• Add native library dependencies needed for cargo doc
• Build rustdoc with --document-private-items for full coverage
• Add internals.md page listing all crates with rustdoc links
• Update Justfile to build from repo root for cargo access

Assisted-by: OpenCode (Opus 4.5)

[gemini-code-assist]

Code Review

This pull request effectively integrates rustdoc generation for internal crates into the documentation website. The changes to the Justfile and docs/Dockerfile.mdbook are well-reasoned to accommodate the new build steps, and the new internals.md page provides a clear entry point to the API documentation. I have one suggestion to improve the Docker build caching for the documentation, which should speed up the process on subsequent runs.

[jeckersb]

👍 LGTM, tested with a local build and a bit of clicky click to sanity check the links work.

[cgwalters]

tested with a local build

Thanks for doing that! I had done so myself as well, but with things like this having human eyes on it is useful as it's harder to "statically" check.

BTW I had AI do the initial pass at this and it ended up doing lots of stuff in the GHA workflow and I told it "no all work needs to be in the Justfile and container build" for precisely this reason of making it easy to run locally too.

I'm pretty happy with how the Justfile stuff is working out.

[cgwalters]

Cool, it's live https://bootc-dev.github.io/bootc/internals.html