feat: support disabling workbench load balancing via Site CR

Problem

Workbench load balancing is hardcoded to enabled (load-balancing-enabled: 1) in site_controller_workbench.go:131. This causes the operator to always create a shared-storage PVC (<site>-workbench-shared-storage) that requires a StorageClass matching the VolumeSource naming convention (e.g. <site>-workbench-shared-storage-nfs).

When managing storage directly (setting volume.storageClassName rather than using a Site-level VolumeSource), this PVC references a StorageClass that doesn't exist, preventing workbench from starting.

Proposed Solution

Add a loadBalancingEnabled field to InternalWorkbenchSpec in site_types.go:

// LoadBalancingEnabled enables workbench load balancing with shared storage.
// Defaults to true. Set to false to disable shared-storage PVC creation
// and load-balancer init containers.
LoadBalancingEnabled *bool `json:"loadBalancingEnabled,omitempty"`

In site_controller_workbench.go, default to true (preserving current behavior) but respect false by setting LoadBalancingEnabled: 0 and ServerSharedStoragePath: "" on the generated Workbench resource.

Affected Code

• api/core/v1beta1/site_types.go — add field to InternalWorkbenchSpec
• internal/controller/core/site_controller_workbench.go — read field, conditionally set rserver config
• internal/controller/core/workbench.go:684 — shared-storage PVC creation (already gated on LoadBalancingEnabled)
• internal/controller/core/workbench.go:1046 — isLoadBalancingEnabled (already gated)

Usage

spec:
  workbench:
    loadBalancingEnabled: false    # disables shared-storage PVC and LB init containers
    volume:
      create: true
      size: 10Gi
      storageClassName: nfs
      accessModes:
        - ReadWriteMany

Start with api/core/v1beta1/site_types.go and internal/controller/core/site_controller_workbench.go, then inspect the existing gates at internal/controller/core/workbench.go:684 and :1046. Confirm how the generated Workbench resource is configured and verify that the default preserves current behavior while false prevents shared-storage PVC and load-balancer init-container creation.