Add Doxyfile and publish API docs (comments are already Doxygen-style)

[OldCrow]

Summary

All public headers in libew and ewpresenter already use Doxygen-style /// comments, but no Doxyfile or published API reference exists. The comments are invisible to users who don't read the source.

Action needed

1. Add a Doxyfile (or docs/Doxyfile) configured for:

   • INPUT = libew/include ewpresenter/include
   • HTML output to docs/html/ (gitignored)
   • EXTRACT_ALL = NO (only document explicitly commented symbols)
   • GENERATE_LATEX = NO

2. Add a docs CI job (or post-build step) that:

   • Runs doxygen Doxyfile
   • Optionally publishes to GitHub Pages on tag pushes.

3. Update README.md to link to the published docs (or instruct how to build them locally).

Files

• Doxyfile — new at repo root (or docs/Doxyfile)
• .github/workflows/ci.yml — optional docs publish job
• README.md — link to docs