Complete notification expiry and configurable durable delivery (#36)

backend/notifications/config.example.yml

@@ -22,3 +22,13 @@ email:
     api_key_env: "RESEND_API_KEY" # SENDGRID_API_KEY when driver is sendgrid
     sender_address: "notifications@example.com"
     sender_name: "SXCHNGE"
+
+# Use replicas: 3 and environment: production for a three-node NATS cluster.
+# mode: ops validates resources without modifying them; app provisions them.
+queue:
+  stream:
+    replicas: 1
+    max_age_hours: 48
+  provisioning:
+    mode: app
+    environment: non-production