fix: add python3 to ISO packages for Claude API proxy

The claude-api-proxy.py requires python3 which was missing from the
rootfs package list, breaking AIUI on fresh installs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

image-recipe/build-auto-installer-iso.sh

@@ -260,6 +260,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     slirp4netns \
     fuse-overlayfs \
     tor \
+    python3 \
     curl \
     git \
     vim-tiny \
@@ -283,6 +284,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     plymouth \
     plymouth-themes \
     zstd \
+    python3 \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*