[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.Infrastructure/Persistence/ApplicationDbContext.cs

@@ -5,6 +5,7 @@ using SolutionErp.Domain.Contracts;
 using SolutionErp.Domain.Forms;
 using SolutionErp.Domain.Identity;
 using SolutionErp.Domain.Master;
+using SolutionErp.Domain.Notifications;
 
 namespace SolutionErp.Infrastructure.Persistence;
 
@@ -25,6 +26,7 @@ public class ApplicationDbContext
     public DbSet<ContractComment> ContractComments => Set<ContractComment>();
     public DbSet<ContractAttachment> ContractAttachments => Set<ContractAttachment>();
     public DbSet<ContractCodeSequence> ContractCodeSequences => Set<ContractCodeSequence>();
+    public DbSet<Notification> Notifications => Set<Notification>();
 
     protected override void OnModelCreating(ModelBuilder builder)
     {

src/Backend/SolutionErp.Infrastructure/Persistence/Configurations/NotificationConfiguration.cs

@@ -0,0 +1,21 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+using SolutionErp.Domain.Notifications;
+
+namespace SolutionErp.Infrastructure.Persistence.Configurations;
+
+public class NotificationConfiguration : IEntityTypeConfiguration<Notification>
+{
+    public void Configure(EntityTypeBuilder<Notification> e)
+    {
+        e.ToTable("Notifications");
+        e.HasKey(x => x.Id);
+        e.Property(x => x.Type).HasConversion<int>();
+        e.Property(x => x.Title).HasMaxLength(300).IsRequired();
+        e.Property(x => x.Description).HasMaxLength(1000);
+        e.Property(x => x.Href).HasMaxLength(500);
+
+        e.HasIndex(x => new { x.UserId, x.ReadAt });
+        e.HasIndex(x => x.CreatedAt);
+    }
+}

src/Backend/SolutionErp.Infrastructure/Persistence/Migrations/20260421082148_AddNotifications.cs

@@ -0,0 +1,54 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace SolutionErp.Infrastructure.Persistence.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddNotifications : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "Notifications",
+                columns: table => new
+                {
+                    Id = table.Column<Guid>(type: "uniqueidentifier", nullable: false),
+                    UserId = table.Column<Guid>(type: "uniqueidentifier", nullable: false),
+                    Type = table.Column<int>(type: "int", nullable: false),
+                    Title = table.Column<string>(type: "nvarchar(300)", maxLength: 300, nullable: false),
+                    Description = table.Column<string>(type: "nvarchar(1000)", maxLength: 1000, nullable: true),
+                    Href = table.Column<string>(type: "nvarchar(500)", maxLength: 500, nullable: true),
+                    ReadAt = table.Column<DateTime>(type: "datetime2", nullable: true),
+                    RefId = table.Column<Guid>(type: "uniqueidentifier", nullable: true),
+                    CreatedAt = table.Column<DateTime>(type: "datetime2", nullable: false),
+                    UpdatedAt = table.Column<DateTime>(type: "datetime2", nullable: true),
+                    CreatedBy = table.Column<Guid>(type: "uniqueidentifier", nullable: true),
+                    UpdatedBy = table.Column<Guid>(type: "uniqueidentifier", nullable: true)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_Notifications", x => x.Id);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_Notifications_CreatedAt",
+                table: "Notifications",
+                column: "CreatedAt");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_Notifications_UserId_ReadAt",
+                table: "Notifications",
+                columns: new[] { "UserId", "ReadAt" });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "Notifications");
+        }
+    }
+}

src/Backend/SolutionErp.Infrastructure/Persistence/Migrations/ApplicationDbContextModelSnapshot.cs

@@ -879,6 +879,58 @@ namespace SolutionErp.Infrastructure.Persistence.Migrations
                     b.ToTable("Suppliers", (string)null);
                 });
 
+            modelBuilder.Entity("SolutionErp.Domain.Notifications.Notification", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uniqueidentifier");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime2");
+
+                    b.Property<Guid?>("CreatedBy")
+                        .HasColumnType("uniqueidentifier");
+
+                    b.Property<string>("Description")
+                        .HasMaxLength(1000)
+                        .HasColumnType("nvarchar(1000)");
+
+                    b.Property<string>("Href")
+                        .HasMaxLength(500)
+                        .HasColumnType("nvarchar(500)");
+
+                    b.Property<DateTime?>("ReadAt")
+                        .HasColumnType("datetime2");
+
+                    b.Property<Guid?>("RefId")
+                        .HasColumnType("uniqueidentifier");
+
+                    b.Property<string>("Title")
+                        .IsRequired()
+                        .HasMaxLength(300)
+                        .HasColumnType("nvarchar(300)");
+
+                    b.Property<int>("Type")
+                        .HasColumnType("int");
+
+                    b.Property<DateTime?>("UpdatedAt")
+                        .HasColumnType("datetime2");
+
+                    b.Property<Guid?>("UpdatedBy")
+                        .HasColumnType("uniqueidentifier");
+
+                    b.Property<Guid>("UserId")
+                        .HasColumnType("uniqueidentifier");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("CreatedAt");
+
+                    b.HasIndex("UserId", "ReadAt");
+
+                    b.ToTable("Notifications", (string)null);
+                });
+
             modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<System.Guid>", b =>
                 {
                     b.HasOne("SolutionErp.Domain.Identity.Role", null)