fix(deploy): copy package.json into subdirs and run npm with --prefix to handle monorepo-like layout

deploy/Dockerfile.frontend

@@ -1,9 +1,9 @@
 FROM node:20-alpine AS builder
 WORKDIR /app
-COPY frontend/package*.json ./
-# Use npm ci when lockfile exists, fallback to npm install
-RUN sh -c 'if [ -f package-lock.json ] || [ -f npm-shrinkwrap.json ]; then npm ci; else npm install; fi'
-COPY frontend/ ./
+COPY frontend/package*.json frontend/
+# Use npm ci when lockfile exists in frontend, fallback to npm install
+RUN sh -c 'if [ -f frontend/package-lock.json ] || [ -f frontend/npm-shrinkwrap.json ]; then npm ci --prefix frontend; else npm install --prefix frontend; fi'
+COPY frontend/ frontend/
 RUN npm run build --prefix frontend
 
 FROM nginx:stable-alpine