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

nginx.conf

@@ -1,5 +1,5 @@
 # Custom nginx config (used by the Dockerfile).
-# Serves the static dashboard with sensible caching + security headers.
+# Serves the static dashboard and proxies /api/chat to the Node API backend.
 
 server {
     listen       80;
@@ -8,6 +8,36 @@ server {
     root   /usr/share/nginx/html;
     index  index.html;
 
+    # Generated data feed; refresh frequently.
+    location = /data.json {
+        add_header Cache-Control "no-cache" always;
+    }
+
+    # Open WebUI chat proxy.
+    location /api/chat {
+        proxy_pass         http://127.0.0.1:3001;
+        proxy_http_version 1.1;
+        proxy_set_header   Host $host;
+        proxy_set_header   X-Real-IP $remote_addr;
+        proxy_read_timeout 120s;
+    }
+
+    # GPU stats proxy (forwarded through the Node backend).
+    location /api/gpu-stats {
+        proxy_pass         http://127.0.0.1:3001;
+        proxy_http_version 1.1;
+        proxy_set_header   Host $host;
+        proxy_read_timeout 15s;
+    }
+
+    # Ollama loaded-model stats proxy.
+    location /api/ollama {
+        proxy_pass         http://127.0.0.1:3001;
+        proxy_http_version 1.1;
+        proxy_set_header   Host $host;
+        proxy_read_timeout 15s;
+    }
+
     location / {
         try_files $uri $uri/ =404;
     }