docs: align public API inventory with crate exports

[e54-bot]

Summary

• Align the public API inventory with every crate-root module and re-export declared in crates/workshop-rs/src/lib.rs.
• Replace the stale source-layout claim that retired compatibility paths remain documentation-hidden support surfaces.
• Link the API inventory from the documentation indexes and release compatibility guidance.
• Fix two rustdoc links found while building the API reference.

Validation

• cargo doc --no-deps -p workshop-rs — passed without warnings.
• git diff --check — passed.
• Tests were not run; this follow-up changes documentation and rustdoc links only.

Fixes #253