feat(crawler): CRAWLER_CHROMIUM_BINARY to use system chromium (0.45.0)

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>

docker-compose.yml

@@ -39,6 +39,11 @@ services:
       # Upload limits.
       MAX_REQUEST_BYTES: ${MAX_REQUEST_BYTES:-209715200}
       MAX_FILE_BYTES: ${MAX_FILE_BYTES:-20971520}
+      # System-chromium override for the crawler. Leave blank to use the
+      # bundled fetcher; set to e.g. /usr/bin/chromium-headless-shell on
+      # arm64 deployments. Pair with `--build-arg INSTALL_CHROMIUM=true`
+      # so the image actually contains the binary.
+      CRAWLER_CHROMIUM_BINARY: ${CRAWLER_CHROMIUM_BINARY:-}
     volumes:
       - storage-data:/var/lib/mangalord/storage
     # No host port mapping in the default setup — the frontend proxies