fix: use RUN --network=host for npm ci in BuildKit

BuildKit sandbox DNS cannot resolve registry.npmjs.org. Using
--network=host on the RUN step lets npm use the host network stack
directly, bypassing the broken sandbox DNS.

frontend/Dockerfile

@@ -1,9 +1,10 @@
+# syntax=docker/dockerfile:1
 # Stage 1: Build
 # Base images: uses Harbor proxy cache in CI, falls back to Docker Hub externally
 FROM registry.celestium.life/dockerhub-cache/library/node:24-alpine AS build
 WORKDIR /app
 COPY package.json package-lock.json ./
-RUN echo "nameserver 8.8.8.8" > /etc/resolv.conf && echo "nameserver 1.1.1.1" >> /etc/resolv.conf && npm ci
+RUN --network=host npm ci
 COPY . .
 ARG VITE_QUERY_API_URL=""
 ARG VITE_SYMBOL_REGISTRY_URL=""