Clear doc-block warnings so doxygen exits 0, add GitHub Actions
for host tests, Doxygen, and manual sync, and document CI in the manual.
Co-authored-by: Cursor <cursoragent@cursor.com>
Add ch-api.tex for REST endpoints and boot flow, update ch-firmware,
ch-build, and ch-intro. Extend CONTRIBUTING, instructions, and README
with manual sync checks and API reference.
Co-authored-by: Cursor <cursoragent@cursor.com>