fix: use npm install in Dockerfile frontend-builder stage (no lockfile)

Same fix as the CI workflow — `npm ci` requires package-lock.json and we
don't track one. Missed this in the earlier CI fix. Local `docker compose
up` builds now succeed past the frontend stage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -3,7 +3,10 @@
 FROM node:22-alpine AS frontend-builder
 WORKDIR /build
 COPY frontend/package.json frontend/package-lock.json* ./
-RUN npm ci --no-audit --no-fund
+# No package-lock.json is tracked yet (we don't run npm locally per
+# feedback-no-local-runs), so `npm install` instead of `npm ci`. Flip to
+# `npm ci` once a lockfile is committed.
+RUN npm install --no-audit --no-fund
 COPY frontend/ ./
 RUN npm run build