fix: correct storage Instance field to match node.Instance in mock data

Previously, storage Instance fields were set to `fmt.Sprintf("pve-%s", node.Name)`,
creating values like "pve-pve1" that didn't match the parent node's Instance field
("mock-cluster"). This caused storage filtering and counting to fail when matching
by instance + node, similar to the backup/snapshot issue fixed earlier.

Changes:
- Set storage.Instance = node.Instance for local storage (generator.go:862)
- Set storage.Instance = node.Instance for local-zfs storage (generator.go:909)
- Set storage.Instance = node.Instance for random storage (generator.go:934)
- PBS storage already correctly used node.Instance (generator.go:969)

This ensures storage counts display correctly on the Storage tab node summary cards
and that filtering by instance + node works consistently across all resource types.

Note: This is part of the broader pattern fix where all resources must match by
both instance AND node name to handle duplicate hostnames across clusters correctly.

internal/mock/generator.go

@@ -859,7 +859,7 @@ func generateStorage(nodes []models.Node) []models.Storage {
 			ID:       fmt.Sprintf("%s-local", node.Name),
 			Name:     "local",
 			Node:     node.Name,
-			Instance: fmt.Sprintf("pve-%s", node.Name),
+			Instance: node.Instance,
 			Type:     "dir",
 			Status:   "available",
 			Total:    localTotal,
@@ -906,7 +906,7 @@ func generateStorage(nodes []models.Node) []models.Storage {
 			ID:       fmt.Sprintf("%s-local-zfs", node.Name),
 			Name:     "local-zfs",
 			Node:     node.Name,
-			Instance: fmt.Sprintf("pve-%s", node.Name),
+			Instance: node.Instance,
 			Type:     "zfspool",
 			Status:   "available",
 			Total:    zfsTotal,
@@ -931,7 +931,7 @@ func generateStorage(nodes []models.Node) []models.Storage {
 				ID:       fmt.Sprintf("%s-%s", node.Name, storageName),
 				Name:     storageName,
 				Node:     node.Name,
-				Instance: fmt.Sprintf("pve-%s", node.Name),
+				Instance: node.Instance,
 				Type:     storageType,
 				Status:   "available",
 				Total:    total,