Add backend data aggregator and API proxy services

- update-data.js: cron job that aggregates Google Calendar ICS feeds
  (today + upcoming, node-ical), Netbird reachability, Gitea/GitLab
  commit stats and Open WebUI models into data.json
- server.js: small Node proxy behind nginx exposing /api/chat
  (Open WebUI completions), /api/gpu-stats and /api/ollama
- gitlab-relay.js: prepared HTTP relay for GitLab over a Netbird VPN
  (not wired up yet; the setup key was rejected by vpn.ixsol.at)
- docker-entrypoint.sh: starts updater in the background, API proxy,
  cron (15 min refresh) and nginx without blocking startup
- nginx: proxy locations + no-cache for data.json
- compose: TZ, token env wiring from .env, gpu-stats service
  (python + rocm-smi with device passthrough)
- dockerignore: keep .env out of the build context

.dockerignore

@@ -1,5 +1,7 @@
 .git
 .gitignore
+.env
+node_modules
 *.md
 .dockerignore
 docker-compose.yml