Docs: add open issues + PRs and missing modules to README table

[taylortom]

Docs

• Renamed the "Dependency test status" section to "Module status" and updated its caption.
• Added Open issues and Open PRs columns (live shields.io badges) alongside the existing Tests badge for every module.
• Added three modules that were missing from the table:
  • `adapt-authoring-api`
  • `adapt-authoring-langpack-en` (data-only langpack — no `tests.yml`, Tests cell shows `—`)
  • `adapt-authoring-usergroups`

Excluded (not runtime modules, consistent with the table's existing scope): `adapt-authoring-documentation`, `adapt-authoring-integration-data`, `adapt-authoring-integration-tests`, `zipper`.