Refactor backend: fix geo cache cleanup, scheduler heartbeat, correlation middleware; update docs

Docs/Deployment.md

@@ -351,6 +351,12 @@ Use native monitoring:
 
 ---
 
+## Configuration
+
+All runtime settings are documented in [CONFIGURATION.md](./CONFIGURATION.md), including database, session, fail2ban, HTTP client, geolocation, CORS, logging, rate limiting, and observability options.
+
+---
+
 ## Environment Variables
 
 Resource limits are configured in `Docker/docker-compose.yml` and cannot be overridden via environment variables. To adjust limits: