Finalize schema reference docs as fully generated (docs repo)

[lowlydba]

Sub-issue of OvertureMaps/schema#679, scoped to the OvertureMaps/docs half of the work.

Drop the committed docs/schema/reference/**/*.md snapshot and the side-by-side auto-gen vs. checked-in comparison build in staging_deploy.yaml. Generate the schema reference docs in every build path instead of reading a committed copy: staging PR previews, ci.yml's a11y job, and the production deploy. Add a schema-ref input to production_deploy_documentation.yml so a schema release can trigger a rebuild against a specific released version.

Implemented in #493.