[CLAUDE] App+Api: 7 Details CRUD endpoints + Changelogs query

## DTOs (Application/Contracts/Dtos/ContractDetailDtos.cs)

- 7 typed DTOs (ThauPhuDetailDto, GiaoKhoanDetailDto, NhaCungCapDetailDto,
  DichVuDetailDto, MuaBanDetailDto, NguyenTacNccDetailDto,
  NguyenTacDvDetailDto) — schema 1-1 với Domain entities
- ContractDetailsBundleDto — wrapper trả về theo Type, chỉ 1 list có data
  (FE đọc field tương ứng, tránh polymorphic deserialize phức tạp)
- ContractChangelogDto — full audit entry

## CQRS (Application/Contracts/ContractDetailsFeatures.cs)

- GetContractDetailsQuery — load bundle, switch theo Contract.Type chỉ
  query bảng tương ứng (avoid 7 query waste)
- 7 AddXxxDetailCommand handlers — typed payload + EnsureContractType
  guard (throw ConflictException nếu Contract.Type sai)
- DeleteContractDetailCommand generic — dispatch xóa theo Type, log change
- Tất cả handler call IChangelogService.LogDetailChangeAsync với summary
  human-readable (vd "Thêm hạng mục: Đào móng")

## CQRS (Application/Contracts/ContractChangelogFeatures.cs)

- ListContractChangelogsQuery (read-only) — desc CreatedAt, default top 200

## Controller (Api/Controllers/ContractsController.cs)

8 endpoints mới:
- GET /api/contracts/{id}/details → bundle theo Type
- POST /api/contracts/{id}/details/{thau-phu|giao-khoan|nha-cung-cap|
  dich-vu|mua-ban|nguyen-tac-ncc|nguyen-tac-dv} → 7 typed POST
- DELETE /api/contracts/{id}/details/{detailId} → generic delete
- GET /api/contracts/{id}/changelogs → list audit entries

Build: dotnet pass (0 error)

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

src/Backend/SolutionErp.Application/Contracts/Dtos/ContractDetailDtos.cs

@@ -0,0 +1,47 @@
+using SolutionErp.Domain.Contracts;
+
+namespace SolutionErp.Application.Contracts.Dtos;
+
+// 7 typed DTOs cho 7 ContractType-specific Details bảng. Map 1-1 với entity
+// trong Domain/Contracts/Details/. Generic ContractDetailItem dùng cho
+// list-mixed view (vd Lịch sử changelog reference).
+
+public record ThauPhuDetailDto(Guid Id, int Order, string HangMuc, string DonViTinh, decimal KhoiLuong, decimal DonGia, decimal ThanhTien, DateTime? ThoiGianHoanThanh, string? GhiChu);
+
+public record GiaoKhoanDetailDto(Guid Id, int Order, string MaCongViec, string TenCongViec, string DonViTinh, decimal KhoiLuong, decimal DonGia, decimal ThanhTien, DateTime? ThoiGianHoanThanh, string? YeuCauKyThuat, string? GhiChu);
+
+public record NhaCungCapDetailDto(Guid Id, int Order, string MaSP, string TenSP, string? ThongSoKyThuat, string DonViTinh, decimal SoLuong, decimal DonGia, decimal ThanhTien, DateTime? ThoiGianGiao, string? XuatXu, string? GhiChu);
+
+public record DichVuDetailDto(Guid Id, int Order, string MaDichVu, string TenDichVu, string? MoTa, string DonViTinh, decimal ThoiGian, decimal DonGia, decimal ThanhTien, DateTime? TuNgay, DateTime? DenNgay, string? GhiChu);
+
+public record MuaBanDetailDto(Guid Id, int Order, string MaSP, string TenSP, string? MoTa, string DonViTinh, decimal SoLuong, decimal DonGia, decimal ThueVAT, decimal ThanhTien, string? XuatXu, string? GhiChu);
+
+public record NguyenTacNccDetailDto(Guid Id, int Order, string NhomSP, string TenSP, string DonViTinh, decimal DonGiaToiThieu, decimal DonGiaToiDa, string? DieuKienGiaoHang, string? DieuKienThanhToan, string? GhiChu);
+
+public record NguyenTacDvDetailDto(Guid Id, int Order, string LoaiDichVu, string TenDichVu, string DonViTinh, decimal DonGiaToiThieu, decimal DonGiaToiDa, string? PhamViDichVu, string? SLA, string? GhiChu);
+
+// Wrapper trả về theo Type — FE đọc field tương ứng (chỉ 1 list có data,
+// 6 list khác empty). Tránh dùng object/dynamic — TS strict mode.
+public record ContractDetailsBundleDto(
+    ContractType Type,
+    List<ThauPhuDetailDto> ThauPhu,
+    List<GiaoKhoanDetailDto> GiaoKhoan,
+    List<NhaCungCapDetailDto> NhaCungCap,
+    List<DichVuDetailDto> DichVu,
+    List<MuaBanDetailDto> MuaBan,
+    List<NguyenTacNccDetailDto> NguyenTacNcc,
+    List<NguyenTacDvDetailDto> NguyenTacDv);
+
+// Changelog DTO cho FE Lịch sử tab
+public record ContractChangelogDto(
+    Guid Id,
+    ChangelogEntityType EntityType,
+    Guid? EntityId,
+    ChangelogAction Action,
+    ContractPhase? PhaseAtChange,
+    Guid? UserId,
+    string? UserName,
+    string? Summary,
+    string? FieldChangesJson,
+    string? ContextNote,
+    DateTime CreatedAt);