fix(docker): add passwd package for useradd on ubuntu:24.04

Ubuntu 24.04 minimal doesn't include passwd (useradd/groupadd).
Debian bookworm-slim had it by default. Required for foxhunt user.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infra/docker/Dockerfile.foxhunt-runtime

@@ -12,6 +12,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     curl \
     jq \
     unzip \
+    passwd \
     && curl -fsSL https://downloads.rclone.org/v1.69.1/rclone-v1.69.1-linux-amd64.zip -o /tmp/rclone.zip \
     && unzip -j /tmp/rclone.zip '*/rclone' -d /usr/local/bin/ \
     && rm /tmp/rclone.zip \