Chrome/Chromium on Linux use ~/.pki/nssdb, not only
update-ca-certificates. Auto-install now runs both paths.
- certificate_authority.js: installLinuxRootCA + certutil for
user NSS (~/.pki/nssdb) and optional /etc/pki/nssdb
- docs/CERTIFICATES.md: manual steps (libnss3-tools, certutil, verify)
- docs/README_LONGFORM.md, EXAMPLES.md, README.md: aligned Linux instructions