fix: use npm install instead of npm ci (no package-lock.json yet)

Switch back to npm ci once package-lock.json is committed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/Dockerfile

@@ -3,7 +3,7 @@ FROM node:20-alpine AS frontend-builder
 
 WORKDIR /app/frontend
 COPY frontend/package*.json ./
-RUN npm ci
+RUN npm install
 COPY frontend/ ./
 RUN npm run build