fix: support host UID/GID mapping for volume mounts

- Add USER_UID/USER_GID build args to Dockerfile
- Install gosu and remap node user/group at build time
- Set node home directory to /paperclip so agent credentials resolve correctly
- Add docker-entrypoint.sh for runtime UID/GID remapping via gosu

Co-Authored-By: Paperclip <noreply@paperclip.ing>

docker-entrypoint.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+set -e
+
+# Capture runtime UID/GID from environment variables, defaulting to 1000
+PUID=${USER_UID:-1000}
+PGID=${USER_GID:-1000}
+
+# Adjust the node user's UID/GID if they differ from the runtime request
+# and fix volume ownership only when a remap is needed
+changed=0
+
+if [ "$(id -u node)" -ne "$PUID" ]; then
+    echo "Updating node UID to $PUID"
+    usermod -o -u "$PUID" node
+    changed=1
+fi
+
+if [ "$(id -g node)" -ne "$PGID" ]; then
+    echo "Updating node GID to $PGID"
+    groupmod -o -g "$PGID" node
+    usermod -g "$PGID" node
+    changed=1
+fi
+
+if [ "$changed" = "1" ]; then
+    chown -R node:node /paperclip
+fi
+
+exec gosu node "$@"