refactor: use CAMELEER_SERVER_URL for agent export endpoint

The runtime-base image and all agent Dockerfiles now read
CAMELEER_SERVER_URL instead of CAMELEER_EXPORT_ENDPOINT.
Updated the volume-mode entrypoint override to match.

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

cameleer3-server-app/src/main/java/com/cameleer3/server/app/runtime/DockerRuntimeOrchestrator.java

@@ -108,7 +108,7 @@ public class DockerRuntimeOrchestrator implements RuntimeOrchestrator {
             createCmd.withEntrypoint("sh", "-c",
                     "exec java -javaagent:/app/agent.jar " +
                     "-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} " +