fix: use public npm registry in sync builder to avoid Apple registry failures

npm.apple.com causes silent install failures for devDependencies inside
the Docker build context. Explicitly use registry.npmjs.org for the
builder stage.

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

sync/Dockerfile

@@ -2,7 +2,7 @@
 FROM node:20-slim AS builder
 WORKDIR /app
 COPY package.json package-lock.json ./
-RUN NODE_ENV=development npm install && ls node_modules/.bin/tsc && echo "tsc OK"
+RUN NODE_ENV=development npm install --registry https://registry.npmjs.org
 COPY tsconfig.json ./
 COPY src ./src
 RUN ./node_modules/.bin/tsc && npm prune --production