Skips the chromiumoxide fetcher when CRAWLER_CHROMIUM_BINARY is set,
unblocking Linux_arm64 deployments (Raspberry Pi 5) where the
fetcher's upstream snapshot bucket has no reliable build. The
Dockerfile gains an INSTALL_CHROMIUM build-arg that adds
chromium-headless-shell + fonts-liberation to the runtime image when
set; default off so cloud/x86 images stay slim.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>