Add centralized include for Access-Control-Allow headers across proxy/service Nginx templates and align ACA vars for simpleicons task.

Ref: https://chatgpt.com/share/68dbf59c-f424-800f-aa27-787db52e260f

roles/sys-svc-proxy/templates/location/html.conf.j2

@@ -19,6 +19,8 @@ location {{location}}
 
   {% include 'roles/sys-svc-proxy/templates/headers/content_security_policy.conf.j2' %}
 
+  {% include 'roles/sys-svc-proxy/templates/headers/access_control_allow.conf.j2' %}
+
   # WebSocket specific header
   proxy_http_version 1.1;
   proxy_set_header Upgrade $http_upgrade;