Introduce core multi-cluster support in the Playwright framework so setup and tests can target manager or managed cluster via a single orchestrator for Fleet Virtualization runs. Single-cluster behavior remains the default when no managed clusters are configured.

As a test maintainer, I want a ClusterOrchestrator that registers manager and managed clusters and provides cluster-specific auth to drivers and clients, so that Fleet Virtualization tests and setup can run against ACM topologies without hard-coding cluster selection.