refactor: rename CAMELEER_EXPORT_ENDPOINT to CAMELEER_SERVER_URL in runtime-base

Standardize env var naming. The agent reads CAMELEER_SERVER_URL
to configure -Dcameleer.export.endpoint.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/runtime-base/Dockerfile

@@ -7,7 +7,7 @@ COPY agent.jar /app/agent.jar
 
 ENTRYPOINT exec java \
   -Dcameleer.export.type=${CAMELEER_EXPORT_TYPE:-HTTP} \
-  -Dcameleer.export.endpoint=${CAMELEER_EXPORT_ENDPOINT} \
+  -Dcameleer.export.endpoint=${CAMELEER_SERVER_URL} \
   -Dcameleer.agent.name=${HOSTNAME} \
   -Dcameleer.agent.application=${CAMELEER_APPLICATION_ID:-default} \
   -Dcameleer.agent.environment=${CAMELEER_ENVIRONMENT_ID:-default} \