[CLAUDE] Domain+App+Infra: Plan B Chunk C — Mig 33 ContractLevelOpinions cookie-cutter mirror PE Mig 26

- Domain/Contracts/ContractLevelOpinion.cs (NEW entity mirror PE — AuditableEntity, 4 field core + 2 nav)
- Domain/Contracts/Contract.cs (+LevelOpinions nav collection)
- Migrations/20260522052240_AddContractLevelOpinions.cs (3-file rule: .cs + .Designer.cs + Snapshot)
- Configurations/ContractLevelOpinionConfiguration.cs (NEW separate file, mirror PE pattern)
- IApplicationDbContext.cs + ApplicationDbContext.cs (+DbSet<ContractLevelOpinion>)

UNIQUE composite (ContractId, ApprovalWorkflowLevelId) — 1 row per HĐ × Level.
FK Cascade Contract + Restrict ApprovalWorkflowLevel.
SignedByUserId KHÔNG nav (denorm SignedByFullName tránh cascade khi xoá user).

Mirror PE Mig 26 pattern (S19 2026-05-09) EXACT — UPSERT row khi Approver duyệt qua
Service ApproveV2Async (Plan B Chunk B em main 138469d đã có TODO marker).
Em main sẽ add UPSERT block sau Chunk C done (Chunk D).

Verify:
- dotnet build PASS 0 err (2 pre-existing warn DocxRenderer unrelated)
- dotnet ef database update PASS (Mig 33 applied SolutionErp_Dev + _Design)
- dotnet test 111/111 PASS (58 Domain + 53 Infra — no regression)

Plan B chain (6 chunks):
- A1 58898e8 ✅ ContractApprovalWorkflowV2 entity scaffold
- A2 a85e437 ✅ Contract.ApprovalWorkflowId + ContractConfiguration FK
- B 138469d ✅ ContractWorkflowService ApproveV2Async skeleton + TODO LevelOpinion UPSERT
- C (this) ✅ ContractLevelOpinions entity + Mig 33 + config + DbSet
- D FE Workspace V2 (Implementer, pending)
- E FE Section 5 V2 (Implementer, pending)

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

src/Backend/SolutionErp.Application/Common/Interfaces/IApplicationDbContext.cs

@@ -35,6 +35,9 @@ public interface IApplicationDbContext
     DbSet<ContractCodeSequence> ContractCodeSequences { get; }
     DbSet<ContractChangelog> ContractChangelogs { get; }
     DbSet<ContractDepartmentApproval> ContractDepartmentApprovals { get; }
+    // Plan B Chunk C (S29 — Mig 33) — Ý kiến cấp duyệt V2 dynamic cho HĐ.
+    // Cookie-cutter mirror PE Mig 26 PurchaseEvaluationLevelOpinions.
+    DbSet<ContractLevelOpinion> ContractLevelOpinions { get; }
     DbSet<Notification> Notifications { get; }
     DbSet<WorkflowTypeAssignment> WorkflowTypeAssignments { get; }
     DbSet<WorkflowDefinition> WorkflowDefinitions { get; }