chore(docs): normalise licensing and consolidate health files

Wave 1 of the documentation standardisation rollout. Mechanical only --
no prose was rewritten, and no file outside the set below was touched.

- Licence body and copyright line normalised to the canonical text in
  willtheorangeguy/.github/licenses, replacing 28 divergent variants.
  Repositories deliberately on GPL-3.0, Apache-2.0, BSD-2 or an upstream
  copyright were left alone.
- Extensionless LICENSE renamed to LICENSE.md for a single convention.
- CONTENT_LICENSE.md added where a repository carries both code and
  content, so the two are licensed separately instead of one blanket
  grant covering material that was not ours to license.
- Duplicated CODE_OF_CONDUCT.md, CONTRIBUTING.md and SECURITY.md removed
  from public repositories, which inherit them from the org-level
  .github repository. Private repositories keep their own copies, since
  org defaults do not reach them.
- README links to those files rewritten to absolute .github URLs in the
  same commit as the deletion, so no link is ever left dangling.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TtaJBmFDK3GcSyuhSuZ84R

Author: willtheorangeguy