Add file package to Docker image for better debugging (#578)

The Docker builds have been failing since June 2025 with the error:
'/bin/bash: line 1: file: command not found'

This error occurs when the SHA256 checksum verification fails and the
Dockerfile attempts to run 'file' command to help debug what type of
file was downloaded. However, the 'file' package is not installed in
the debian:stable-slim base image.

This commit adds the 'file' package to the apt-get install list so that
when SHA256 verification fails, we can get better debugging information
about what was actually downloaded (e.g., whether it's an HTML error
page instead of the expected tar.xz file).

While this doesn't fix the root cause of the SHA256 failures, it will
provide better diagnostics to help identify the actual issue.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Took 55 minutes

Author: fank

docker/Dockerfile

@@ -43,7 +43,7 @@ ENV PORT=34197 \
 SHELL ["/bin/bash", "-eo", "pipefail", "-c"]
 
 RUN apt-get -q update \
-    && DEBIAN_FRONTEND=noninteractive apt-get -qy install ca-certificates curl jq pwgen xz-utils procps gettext-base --no-install-recommends \
+    && DEBIAN_FRONTEND=noninteractive apt-get -qy install ca-certificates curl jq pwgen xz-utils procps gettext-base file --no-install-recommends \
     && if [[ "$(uname -m)" == "aarch64" ]]; then \
         echo "installing ARM compatability layer" \
         && DEBIAN_FRONTEND=noninteractive apt-get -qy install unzip --no-install-recommends \