Updates for grafana stack

playbooks/site.yml

@@ -1,5 +1,9 @@
 ---
-- name: Provision webservers
+# Order: base OS → central Loki/Prometheus/Grafana → Alloy agents.
+# Alloy on every host pushes to the stack on ai-server-4080, so the stack
+# must exist before (or at least as Alloy starts against) those endpoints.
+
+- name: Provision webservers (base)
   hosts: webservers
   become: true
   roles:
@@ -9,3 +13,16 @@
     - nodejs
     - gitea-key
     - tianji
+
+- name: Provision central observability stack
+  hosts: ai-server-4080
+  become: true
+  roles:
+    - role: observability
+      when: observability_stack | default(false) | bool
+
+- name: Provision Alloy agents
+  hosts: webservers
+  become: true
+  roles:
+    - alloy