Fix staging containers failing on Windows Docker builds

Strip CRLF from entrypoint scripts in backend/frontend images, use Docker
DNS in staging nginx config, and wait for healthy app services before nginx.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/Dockerfile

@@ -47,7 +47,8 @@ COPY --from=builder /app/dist ./dist
 COPY --from=builder /app/node_modules ./node_modules
 
 COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
-RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+# Windows git/build context may use CRLF; strip before chmod (fixes dumb-init "No such file or directory").
+RUN sed -i 's/\r$//' /usr/local/bin/docker-entrypoint.sh && chmod +x /usr/local/bin/docker-entrypoint.sh
 
 RUN mkdir -p /app/logs && \
     chown -R dyolink:nodejs /app