[CLAUDE] PurchaseEvaluation: require quy trinh duyet V2 o create+submit (dong lo hong quy-trinh-cu)

Validator NotEmpty(ApprovalWorkflowId) + submit guard (sau Section-3, truoc mutate phase). Dong lo hong validate FE-only -> phieu null-workflow ket nhanh V1-legacy "quy trinh cu" (khong Buoc/Cap, khong route duyet). Test-before (RED confirmed): +2 validator test (PeWorkItemGuardTests) + rewrite test 7/13 PeSubmitGuardAndBypass (V1-submit deprecated, data V1 wipe S59). 356 pass (45D+311I).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationFeatures.cs

@@ -41,6 +41,12 @@ public class CreatePurchaseEvaluationCommandValidator : AbstractValidator<Create
         // async-db; mirror S43 CreateLeaveRequestHandler FK-invariant guard).
         RuleFor(x => x.WorkItemId).NotEmpty()
             .WithMessage("Phải chọn hạng mục công việc.");
+        // [S83 bug fix] BE enforce quy trình duyệt V2 — đóng lỗ hổng validate
+        // FE-only (FE canSubmit bắt buộc nhưng BE chỉ validate-nếu-có-truyền →
+        // phiếu null-workflow lọt vào ChoDuyet = kẹt V1-legacy "quy trình cũ").
+        // NotEmpty chặn cả null lẫn Guid.Empty.
+        RuleFor(x => x.ApprovalWorkflowId).NotEmpty()
+            .WithMessage("Phải chọn quy trình duyệt.");
         RuleFor(x => x.DiaDiem).MaximumLength(500);
         RuleFor(x => x.MoTa).MaximumLength(2000);
         // [HoSoLink] MaxLength MATCH EF config HasMaxLength(1000) (S35 lesson).