v3 batch1 WP1: greenfield DbContext + V3Initial squash + seeds + tests

DbContext (OtOpcUaConfigDbContext):
- Drop Namespace/EquipmentImportBatch/EquipmentImportRow DbSets + Configure methods.
- Add RawFolder/TagGroup/UnsTagReference DbSets + Configure methods with sibling-name
  filtered unique indexes over nullable parents (two-filtered pattern per level).
- Reshape DriverInstance (RawFolderId + UX_DriverInstance_Folder_Name/_ClusterRoot_Name),
  Tag (required DeviceId, nullable TagGroupId, UX_Tag_Group_Name/_Device_Name, IX_Tag_Device),
  Equipment (drop DriverInstanceId/DeviceId + IX_Equipment_Driver), Device (UX_Device_Driver_Name).

Migration squash -> V3Initial:
- Delete the whole Migrations/ folder; scaffold one V3Initial (applies clean to a fresh DB).
- Port the hand-written procs + AuthorizationGrants into V3Initial.StoredProcedures.cs. The v1
  generation-model procs (ConfigGeneration/GenerationId, dead since V2HostingAlignment) are
  rewritten as v3-schema-valid retirement stubs that preserve the two-role EXECUTE-grant surface
  + AuthorizationTests behaviors; sp_ComputeGenerationDiff now references the v3 tables;
  sp_ReleaseExternalIdReservation ported verbatim.

Compile-fixes for the build gate (Wave-C-owned, minimal + TODO(v3 WP4) markers):
- DraftSnapshot/DraftSnapshotFactory: drop the retired Namespaces list.
- DraftValidator: delete namespace-binding + Galaxy-FullName rules; collision rule now VirtualTag-only.

Seeds -> v3 schema:
- seed-clusters.sql summary SELECTs; all 5 scripts/smoke/seed-*.sql rewritten (DriverInstance
  RawFolderId, Device+DeviceConfig endpoint, Tag DeviceId, UnsTagReference; no ConfigGeneration/
  Namespace/sp_PublishGeneration). Verified: all seeds apply clean against a fresh V3Initial DB.

Tests (Configuration.Tests, 107 pass):
- SchemaComplianceTests rewritten to v3 tables + filtered indexes.
- New RawSchemaIntegrityTests: DB-enforced sibling-name uniqueness per raw level + UnsTagReference
  (Equipment,Tag) uniqueness.
- Delete DraftValidatorGalaxyFullNameCorpusTests (WP2/WP6 replaces); fix DraftValidatorTests +
  DraftSnapshotFactoryTests to v3 shapes; repoint scripting-migration existence test to V3Initial.

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshot.cs

@@ -25,8 +25,9 @@ public sealed class DraftSnapshot
     /// </summary>
     public string? Site { get; init; }
 
-    /// <summary>Gets the list of OPC UA namespaces.</summary>
-    public IReadOnlyList<Namespace> Namespaces { get; init; } = [];
+    // v3: the Namespace entity is retired (the two OPC UA namespaces are implicit). The old
+    // Namespaces list + namespace-binding validation are gone. WP4 (Wave C) owns the new v3
+    // rules (raw-name charset, historized-tagname length, UNS effective-leaf uniqueness).
     /// <summary>Gets the list of driver instances.</summary>
     public IReadOnlyList<DriverInstance> DriverInstances { get; init; } = [];
     /// <summary>Gets the list of devices.</summary>