split docker-compose into core and observability stacks; add ntfy, alertmanager, blackbox exporter, and otel-collector services; configure prometheus alerting pipeline

Caddyfile

@@ -2,6 +2,9 @@
     servers {
         metrics
     }
+    metrics {
+        per_host
+    }
     admin :2019
 }
 
@@ -19,4 +22,8 @@ gitea.qpismont.fr {
 
 woodpecker.qpismont.fr {
 	reverse_proxy woodpecker_server:8000
+}
+
+ntfy.qpismont.fr {
+    reverse_proxy ntfy:80
 }