fix: SQLite readonly error in Docker container

- Add entrypoint script that ensures /data is owned by node user
  before dropping privileges with su-exec
- Remove USER node from Dockerfile (entrypoint handles it)
- Change client depends_on to service_healthy so nginx waits for
  the server to pass its healthcheck before starting

web/server/docker-entrypoint.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+set -e
+
+# Ensure data directory exists and is writable by the node user
+mkdir -p /data
+chown node:node /data
+
+# Drop privileges and exec the CMD
+exec su-exec node "$@"