Wire up visitor metrics from webserver DB and fix uptime monitoring

- Read visitors from /server_storage/visitors.db (webserver's DB) instead of
  admin dash's own table; geoip lookups at query time for globe markers
- Globe card now shows 24h, 7d, and all-time unique visitor counts
- Uptime monitor: Nextcloud via host.docker.internal for Docker networking,
  Website and Gitea monitored on public domains
- UptimeCard uses real hourly history bars instead of Math.random() mock
- docker-compose: mount /server_storage:ro, add extra_hosts for Linux compat

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

docker-compose.yml

@@ -5,8 +5,11 @@ services:
     restart: always
     ports:
       - "3333:3000"
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
     environment:
       - NODE_ENV=production
       - DB_PATH=/app/data/dashboard.db
     volumes:
       - ./data:/app/data
+      - /server_storage:/server_storage:ro