feat(proxy): add service CRUD with persistent storage

ServiceManager with JSON file persistence replaces static env var config.
CRUD API endpoints (POST/PUT/DELETE /api/services) with WebSocket broadcast.
Dashboard: add/edit/delete services via modal form.

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

packages/proxy/Dockerfile

@@ -46,5 +46,6 @@ COPY --from=build-proxy /app/packages/proxy/dist packages/proxy/dist
 COPY --from=build-web /app/packages/proxy/web/build packages/proxy/public/dashboard
 
 WORKDIR /app/packages/proxy
+RUN mkdir -p /app/data
 EXPOSE 47391
 CMD ["node", "dist/index.js"]