feat(docker): Add PUID/PGID support for volume permissions

Introduces a robust entrypoint script and 'gosu' to allow users to specify
Process User ID (PUID) and Process Group ID (PGID) via environment variables.

This resolves permission errors encountered when binding host volumes into
the container, as the entrypoint script now runs 'chown' on /config and
/metadata as root before dropping privileges and running the application.

- Adds 'gosu' dependency to the runtime stage.
- Implements 'docker-entrypoint.sh' to handle user switching and permission fixing.
- Updates ENTRYPOINT to use the wrapper script, passing CMD as arguments.

Dockerfile

@@ -50,7 +50,8 @@ ARG NUSQLITE3_PATH
 RUN apk add --no-cache --update \
   tzdata \
   ffmpeg \
-  tini
+  tini \
+  gosu
 
 WORKDIR /app
 
@@ -59,6 +60,10 @@ COPY --from=build-client /client/dist /app/client/dist
 COPY --from=build-server /server /app
 COPY --from=build-server ${NUSQLITE3_PATH} ${NUSQLITE3_PATH}
 
+# Copy Entry script and add execute permissions.
+COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
 EXPOSE 80
 
 ENV PORT=80
@@ -69,5 +74,7 @@ ENV SOURCE="docker"
 ENV NUSQLITE3_DIR=${NUSQLITE3_DIR}
 ENV NUSQLITE3_PATH=${NUSQLITE3_PATH}
 
-ENTRYPOINT ["tini", "--"]
+# Call entrypoint script instead of just tini.
+ENTRYPOINT ["tini", "--", "/usr/local/bin/docker-entrypoint.sh"]
+# This becomes the argument ($@) for the entrypoint script
 CMD ["node", "index.js"]

docker-entrypoint.sh

@@ -0,0 +1,51 @@
+#!/bin/sh
+set -e
+
+# --- PUID/PGID Check and Defaults ---
+# Set default PUID/PGID to 1000 if not provided
+PUID=${PUID:-1000}
+PGID=${PGID:-1000}
+
+echo "Starting with PUID: $PUID, PGID: $PGID"
+
+# --- User/Group Setup ---
+# Create or modify the 'appuser' group to match the PGID
+if [ -z "$(getent group "${PGID}")" ]; then
+    addgroup -g "${PGID}" appgroup
+else
+    # Group exists, ensure the name is correct for the PUID/PGID
+    group_name=$(getent group "${PGID}" | cut -d: -f1)
+    if [ "$group_name" != "appgroup" ]; then
+        echo "WARNING: PGID ${PGID} already exists with name ${group_name}. Using existing group."
+        app_group_name="${group_name}"
+    else
+        app_group_name="appgroup"
+    fi
+fi
+
+# Create or modify the 'appuser' user to match the PUID and assign to the PGID
+if [ -z "$(getent passwd "${PUID}")" ]; then
+    adduser -u "${PUID}" -G "${app_group_name:-appgroup}" -D -s /bin/sh appuser
+else
+    # User exists, ensure the name is correct for the PUID/PGID
+    user_name=$(getent passwd "${PUID}" | cut -d: -f1)
+    if [ "$user_name" != "appuser" ]; then
+        echo "WARNING: PUID ${PUID} already exists with name ${user_name}. Using existing user."
+        app_user_name="${user_name}"
+    else
+        app_user_name="appuser"
+    fi
+fi
+
+# --- Permission Fix (Crucial Step) ---
+# This fixes permissions on directories meant for bind mounts (volumes)
+# CONFIG_PATH and METADATA_PATH are the likely mount points
+echo "Fixing permissions on volume paths (${CONFIG_PATH} and ${METADATA_PATH})..."
+chown -R "${PUID}":"${PGID}" "${CONFIG_PATH}" || true
+chown -R "${PUID}":"${PGID}" "${METADATA_PATH}" || true
+
+# --- Execute Main Command ---
+# Use 'gosu' to securely drop privileges and run the main command
+# Pass all arguments ($@) to the final application command
+echo "Executing CMD as user ${PUID}..."
+exec gosu "${PUID}":"${PGID}" "$@"