docs: add project documentation

docs/CONFIGURATION.md

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+# Configuration
+
+## Docker Compose
+
+The root `docker-compose.yml` defines the application container.
+
+Default port mapping:
+
+- Host: `8088`
+- Container: `8080`
+
+Change the port mapping in `docker-compose.yml` if host port `8088` is already in use.
+
+## Application settings
+
+The Spring Boot configuration is maintained in:
+
+`backend/src/main/resources/application.yaml`
+
+Review the actual configuration file before changing application properties. This document intentionally does not assume environment variables or settings that may not exist in the current implementation.
+
+## Container permissions and monitoring scope
+
+System metrics available to the application depend on the operating system, container runtime, mounted filesystems, and granted permissions.
+
+A container does not automatically have complete visibility into its host. Docker Desktop on Windows runs Linux containers in a virtualized Linux environment, so reported metrics may describe that environment rather than Windows itself.
+
+Do not expose the monitoring interface to untrusted networks without appropriate access controls and network security.