fix(docker): run as non-root user, use virtualenv (salvage #5811)

- Add gosu for runtime privilege dropping from root to hermes user
- Support HERMES_UID/HERMES_GID env vars for host mount permission matching
- Switch to debian:13.4-slim base image
- Use uv venv instead of pip install --break-system-packages
- Pin uv and gosu multi-stage images with SHA256 digests
- Set PLAYWRIGHT_BROWSERS_PATH to /opt/hermes/.playwright so build-time
  chromium install survives the /opt/data volume mount
- Keep procps for container debugging

Based on work by m0n5t3r in PR #5811. Stripped to hardening-only
changes (non-root, virtualenv, slim base); matrix deps, fonts, xvfb,
and entrypoint playwright download deferred to follow-up.

docker/entrypoint.sh

@@ -5,6 +5,33 @@ set -e
 HERMES_HOME="/opt/data"
 INSTALL_DIR="/opt/hermes"
 
+# --- Privilege dropping via gosu ---
+# When started as root (the default), optionally remap the hermes user/group
+# to match host-side ownership, fix volume permissions, then re-exec as hermes.
+if [ "$(id -u)" = "0" ]; then
+    if [ -n "$HERMES_UID" ] && [ "$HERMES_UID" != "$(id -u hermes)" ]; then
+        echo "Changing hermes UID to $HERMES_UID"
+        usermod -u "$HERMES_UID" hermes
+    fi
+
+    if [ -n "$HERMES_GID" ] && [ "$HERMES_GID" != "$(id -g hermes)" ]; then
+        echo "Changing hermes GID to $HERMES_GID"
+        groupmod -g "$HERMES_GID" hermes
+    fi
+
+    actual_hermes_uid=$(id -u hermes)
+    if [ "$(stat -c %u "$HERMES_HOME" 2>/dev/null)" != "$actual_hermes_uid" ]; then
+        echo "$HERMES_HOME is not owned by $actual_hermes_uid, fixing"
+        chown -R hermes:hermes "$HERMES_HOME"
+    fi
+
+    echo "Dropping root privileges"
+    exec gosu hermes "$0" "$@"
+fi
+
+# --- Running as hermes from here ---
+source "${INSTALL_DIR}/.venv/bin/activate"
+
 # Create essential directory structure.  Cache and platform directories
 # (cache/images, cache/audio, platforms/whatsapp, etc.) are created on
 # demand by the application — don't pre-create them here so new installs