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

wireguard/CoreDns

@@ -0,0 +1,7 @@
+.:53 {
+    rewrite name perses.internal perses
+    rewrite name prometheus.internal prometheus
+    forward . 127.0.0.11
+    errors
+    cache 10
+}