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

.devcontainer/devcontainer.json

@@ -1,7 +1,6 @@
 {
     "workspaceFolder": "/workspace",
     "workspaceMount": "source=${localWorkspaceFolder},target=/workspace,type=bind,Z",
-    "runArgs": ["--userns=keep-id", "--security-opt", "label=disable"],
     "mounts": [
         "source=${localEnv:HOME}/.ssh,target=/root/.ssh,type=bind,readonly"
     ],