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

docker-compose.yml

@@ -8,6 +8,46 @@ services:
     ports:
       - "8888:80"
     restart: unless-stopped
+    environment:
+      # Timezone used for the "Today" calendar widget.
+      - TZ=Europe/Vienna
+      # Secrets live in .env (gitignored) — compose reads it automatically.
+      - OPENWEBUI_TOKEN=${OPENWEBUI_TOKEN:-}
+      # Optional API tokens for live stats / git integration.
+      # Uncomment and fill in to enable private git stats.
+      # - GITEA_TOKEN=
+      # - GITLAB_TOKEN=
+      # - NETBIRD_TOKEN=
+      # GPU stats upstream; defaults to the gpu-stats service below.
+      # To run gpu_stats.py on the host instead, use:
+      #   http://host.docker.internal:9101/stats
+      # (and add:  extra_hosts: ["host.docker.internal:host-gateway"])
+      # - GPU_STATS_URL=http://gpu-stats:9101/stats
+      # Ollama instance for the loaded-model stats in the GPU widget.
+      # - OLLAMA_URL=http://100.103.83.12:11435
+    logging:
+      driver: json-file
+      options:
+        max-size: "1m"
+        max-file: "2"
+
+  # AMD GPU stats via rocm-smi (gpu_stats.py).
+  # Needs the host's ROCm install + GPU device nodes passed through.
+  gpu-stats:
+    image: python:3.12-slim
+    container_name: homelab-gpu-stats
+    restart: unless-stopped
+    environment:
+      # rocm-smi can't read the device name without libdrm; set it explicitly.
+      - GPU_NAME=AMD Radeon AI PRO R9700
+      # - ROCM_SMI_PATH=/opt/rocm/bin/rocm-smi
+    volumes:
+      - ./gpu_stats.py:/app/gpu_stats.py:ro
+      - /opt/rocm:/opt/rocm:ro
+    devices:
+      - /dev/kfd
+      - /dev/dri
+    command: python3 /app/gpu_stats.py
     logging:
       driver: json-file
       options: