v3 batch1 contracts: RawPaths identity helper + reshaped greenfield entities

Shared-type foundation for Batch 1 fan-out (coordinator contracts commit):
- New Commons/Types/RawPaths.cs — the v3 identity authority (Build/Combine/
  Split/Leaf/TryParent/ValidateSegment, ordinal comparer).
- New entities RawFolder, TagGroup, UnsTagReference.
- Reshape DriverInstance (drop NamespaceId, add nullable RawFolderId),
  Tag (require DeviceId, add nullable TagGroupId, drop DriverInstanceId/
  EquipmentId/FolderPath, keep WriteIdempotent), Equipment (drop
  DriverInstanceId/DeviceId), Device (doc: now universal), ServerCluster
  (nav Namespaces -> RawFolders).
- Delete Namespace, EquipmentImportBatch(+Row), NamespaceKind enum.
- DriverTypeMetadata: drop AllowedNamespaceKinds + NamespaceKindCompatibility.

Solution is intentionally red below the foundation projects until Wave C
integrates. Commons + Core.Abstractions compile green.

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Entities/ServerCluster.cs

@@ -47,6 +47,6 @@ public sealed class ServerCluster
     // Navigation
     /// <summary>Gets or sets the collection of cluster nodes.</summary>
     public ICollection<ClusterNode> Nodes { get; set; } = [];
-    /// <summary>Gets or sets the collection of namespaces in the cluster.</summary>
-    public ICollection<Namespace> Namespaces { get; set; } = [];
+    /// <summary>Gets or sets the collection of root-level Raw-tree folders in the cluster.</summary>
+    public ICollection<RawFolder> RawFolders { get; set; } = [];
 }