fix: add .npmrc to sync service to use public npm registry

The server has an Apple npm proxy that silently drops devDependencies.
Copying the same .npmrc fix used by the frontend (registry=registry.npmjs.org)
resolves the issue.

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

sync/.npmrc

@@ -0,0 +1 @@
+registry=https://registry.npmjs.org/

sync/Dockerfile

@@ -3,7 +3,7 @@ FROM node:20-alpine AS builder
 WORKDIR /app
 ENV PATH="/app/node_modules/.bin:$PATH"
 RUN apk add --no-cache python3 make g++
-COPY package*.json ./
+COPY package*.json .npmrc ./
 RUN npm ci --include=dev
 COPY tsconfig.json ./
 COPY src ./src