Landing page: editions + release links; TOC: add Parts 9-12; drop roadmap

- docs/index.mdx: broaden the intro beyond configuration (module reference,
  recipes, troubleshooting, programming); add a "FreeSWITCH Editions and
  Downloads" section linking the Open Source FreeSWITCH releases and the
  FreeSWITCH Enterprise releases (private repo; needs an Enterprise
  subscription); add navigation to Parts 9-12.
- TABLE-OF-CONTENTS.md: correct the stale scope note (troubleshooting and
  programming are now in scope) and append Parts IX-XII (Module Reference,
  Recipes Ch 33-38, Troubleshooting Ch 39-43, Programming Ch 44-48).
- Remove CONTENT-ROADMAP.md (planning artifact, no longer needed in-tree).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: briankwest