[CLAUDE] Domain: Plan B Chunk A1 — Contract +2 fields V2 (ApprovalWorkflowId + CurrentApprovalLevelOrder)

Mirror PE Mig 22-24 pattern. V1+V2 coexist (7 V1 contract giữ
WorkflowDefinitionId, V2 mới pin ApprovalWorkflowId).

Fields added:
- ApprovalWorkflowId Guid? — pin schema mới ApprovalWorkflowsV2
- CurrentApprovalLevelOrder int? — Cấp đang chờ duyệt (1/2/3) trong Step

Service ApproveV2Async branch (Chunk B) sẽ dispatch:
- if (contract.ApprovalWorkflowId is Guid awId) ApproveV2Async
- else ApproveV1Legacy (giữ behavior 7 V1 contract)

Verify:
- dotnet build SolutionErp.slnx PASS 0 err, 2 pre-existing DocxRenderer warn
- No migration (Chunk A2 sẽ scaffold Mig 32)

Plan B chain (6 chunks):
- A1 (this) Entity +2 fields (em main)
- A2 Mig 32 schema (Implementer Case 2 cookie-cutter)
- B Service ApproveV2Async branch (em main critical ~200 LOC)
- C Mig 33 ContractLevelOpinions (Implementer)
- D FE Workspace V2 (Implementer)
- E FE Section 5 LevelOpinionsV2 (Implementer)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Backend/SolutionErp.Domain/Contracts/Contract.cs

@@ -20,6 +20,7 @@ public class Contract : AuditableEntity
     public string? NoiDung { get; set; }
     public bool BypassProcurementAndCCM { get; set; }              // HĐ Chủ đầu tư → skip CCM
     public Guid? WorkflowDefinitionId { get; set; }                // Pinned at creation — HĐ cũ chạy version cũ ngay cả khi admin active version mới
+    public Guid? ApprovalWorkflowId { get; set; }                  // [Plan B S29 2026-05-22 Mig 32] Pin schema mới ApprovalWorkflowsV2 — mirror PE Mig 23. V1+V2 coexist: 7 V1 contract giữ WorkflowDefinitionId; V2 mới pin ApprovalWorkflowId. Service ApproveV2Async branch theo field này.
     public DateTime? SlaDeadline { get; set; }                     // Hết hạn phase hiện tại
     public string? DraftData { get; set; }                         // JSON field values (render template)
     public bool SlaWarningSent { get; set; }                       // Flag để không gửi warning 2 lần
@@ -39,6 +40,11 @@ public class Contract : AuditableEntity
     public int? CurrentWorkflowStepIndex { get; set; }
     public int? RejectedAtStepIndex { get; set; }
 
+    // [Plan B S29 2026-05-22 Mig 32] V2 workflow tracking — mirror PE Mig 24.
+    // CurrentApprovalLevelOrder: Cấp đang chờ duyệt (1/2/3) trong Step hiện tại
+    // khi pin ApprovalWorkflowId. Null khi V1 legacy hoặc V2 terminal (DaPhatHanh).
+    public int? CurrentApprovalLevelOrder { get; set; }
+
     public List<ContractApproval> Approvals { get; set; } = new();
     public List<ContractComment> Comments { get; set; } = new();
     public List<ContractAttachment> Attachments { get; set; } = new();