fix: declare proxy ARGs in frontend Dockerfile for npm ci

The frontend Dockerfile was missing HTTP_PROXY/HTTPS_PROXY ARG declarations
in the build stage, so npm ci could not reach the npm registry through the
builder's proxy. Same fix pattern as the API Dockerfile.

This explains why the Web image has never been successfully built — the
pipeline always skips 'Build Web' after 'Build API' fails, but once API
build succeeds, Web build would hit the same npm registry issue.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/Dockerfile

@@ -4,6 +4,21 @@ ARG NGINX_IMAGE=nginx:1.27-alpine
 FROM ${NODE_IMAGE} AS build
 WORKDIR /app
 
+# Proxy settings for npm ci / npm run build (npm registry is only reachable
+# via the proxy from the build network).
+ARG HTTP_PROXY
+ARG HTTPS_PROXY
+ARG NO_PROXY
+ARG http_proxy
+ARG https_proxy
+ARG no_proxy
+ENV HTTP_PROXY=${HTTP_PROXY} \
+    HTTPS_PROXY=${HTTPS_PROXY} \
+    NO_PROXY=${NO_PROXY} \
+    http_proxy=${http_proxy} \
+    https_proxy=${https_proxy} \
+    no_proxy=${no_proxy}
+
 COPY package*.json ./
 RUN npm ci