Add Docker socket access configuration for Docker monitoring probes

Configure portable Docker GID support to enable Docker container monitoring in Uptime Kuma. The DOCKER_GID environment variable allows the configuration to work across different servers where the docker group ID may vary.

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -7,6 +7,8 @@ services:
       - no-new-privileges:true
     cap_drop:
       - ALL
+    group_add:
+      - "${DOCKER_GID}"
     networks:
       - traefik-net
     labels: