Refactor EventPublisher and ChatService: replace UUID-based keys with generic unique string keys, add session cleanup callbacks, and update related logic for better extensibility and reusability.

backend/src/main/resources/application.properties

@@ -24,3 +24,4 @@ management.endpoints.web.exposure.include=mappings
 server.forward-headers-strategy=native
 server.tomcat.remoteip.remote-ip-header=CF-Connecting-IP
 server.tomcat.remoteip.trusted-proxies=10\\.0\\.0\\.103
+altitudeweb.token=${TOKEN:invalid-token}