Add Metricbeat integration for system, Docker, and Nginx metrics

- Enable Nginx `stub_status` endpoint on port 8080 for internal metric collection.
- Add Metricbeat configuration for system, Docker, and Nginx metrics, integrating with Elasticsearch and Kibana.

services/metricbeat/metricbeat.yml

@@ -0,0 +1,44 @@
+metricbeat.config.modules:
+  path: ${path.config}/modules.d/*.yml
+  reload.enabled: false
+
+setup.kibana.host: "http://kibana:5601"
+setup.dashboards.enabled: true
+
+output.elasticsearch:
+  hosts: ["http://elasticsearch:9200"]
+
+metricbeat.modules:
+  # System metrics (container-level when running in Docker Desktop)
+  - module: system
+    period: 10s
+    metricsets:
+      - cpu
+      - load
+      - memory
+      - network
+      - process
+      - process_summary
+      - filesystem
+      - fsstat
+      - uptime
+    processes: ['.*']
+
+  # Docker metrics (containers CPU/mem/network, etc.)
+  - module: docker
+    hosts: ["unix:///var/run/docker.sock"]
+    period: 10s
+    enabled: true
+    # Common metricsets: container,cpu,diskio,event,healthcheck,info,memory,network
+    # Use defaults to keep noise reasonable
+
+  # Nginx metrics from stub_status (enabled in nginx.dev.conf on port 8080)
+  - module: nginx
+    metricsets: ["stubstatus"]
+    period: 10s
+    hosts: ["http://nginx:8080/stub_status"]
+    enabled: true
+
+processors:
+  - add_host_metadata: ~
+  - add_docker_metadata: ~

services/nginx/nginx.dev.conf

@@ -71,4 +71,16 @@ http {
         location ~ /\. { deny all; }
         location ~ /\.ht { deny all; }
     }
+
+    # Internal metrics endpoint for Metricbeat (not exposed to host)
+    # Scraped at http://nginx:8080/stub_status by the metricbeat nginx module
+    server {
+        listen 8080;
+        server_name _;
+        access_log off;
+        location /stub_status {
+            stub_status;
+            allow all; # safe within the docker network; not published to host
+        }
+    }
 }