[CLAUDE] App+Domain+Infra+Api+FE: Notifications module end-to-end

Domain:
- Notification entity + NotificationType enum (stable ints)
- Nullable RefId cho correlation (contract, user, ...)

Infrastructure:
- NotificationConfiguration: bảng Notifications, index theo (UserId, ReadAt)
- NotificationService: ghi vào DbContext, không SaveChanges (để caller quyết
  định unit-of-work — đảm bảo atomic với domain mutation)
- EF migration AddNotifications

Application:
- INotificationService (Notify + NotifyMany)
- CQRS: ListMyNotifications / GetMyUnreadCount / MarkRead / MarkAllRead

Api:
- NotificationsController: GET /api/notifications + unread-count + mark-read

Integration:
- ContractWorkflowService emit notification tới Drafter khi HĐ chuyển phase
  (skip nếu actor chính là Drafter). Title + type theo phase đích:
  DaPhatHanh → ContractPublished, TuChoi → ContractRejected, khác →
  ContractPhaseTransition.

FE:
- Both NotificationBell (admin + user) dùng /api/notifications thật
  (thay cho derived-from-inbox MVP trước đó). 30s refetch, click mark-read,
  'Đọc hết' bulk action.

Foundation sẵn cho SignalR push + email outbox sau này — chỉ cần mở rộng
NotificationService mà không đổi caller.

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

src/Backend/SolutionErp.Api/Controllers/NotificationsController.cs

@@ -0,0 +1,35 @@
+using MediatR;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using SolutionErp.Application.Notifications;
+using SolutionErp.Application.Notifications.Dtos;
+
+namespace SolutionErp.Api.Controllers;
+
+[ApiController]
+[Route("api/notifications")]
+[Authorize]
+public class NotificationsController(IMediator mediator) : ControllerBase
+{
+    [HttpGet]
+    public async Task<ActionResult<IReadOnlyList<NotificationDto>>> List(
+        [FromQuery] bool unreadOnly = false,
+        [FromQuery] int limit = 50,
+        CancellationToken ct = default)
+        => Ok(await mediator.Send(new ListMyNotificationsQuery(unreadOnly, limit), ct));
+
+    [HttpGet("unread-count")]
+    public async Task<ActionResult<int>> UnreadCount(CancellationToken ct)
+        => Ok(await mediator.Send(new GetMyUnreadCountQuery(), ct));
+
+    [HttpPost("{id:guid}/read")]
+    public async Task<IActionResult> MarkRead(Guid id, CancellationToken ct)
+    {
+        await mediator.Send(new MarkNotificationReadCommand(id), ct);
+        return NoContent();
+    }
+
+    [HttpPost("read-all")]
+    public async Task<ActionResult<int>> MarkAllRead(CancellationToken ct)
+        => Ok(await mediator.Send(new MarkAllNotificationsReadCommand(), ct));
+}