fix: identity 登录并发改为 xmin

移除 identity_users 对 RowVersion 列的依赖，改用 PostgreSQL xmin 作为并发令牌，修复线上登录因缺失 RowVersion 列导致的 500 错误。

src/Infrastructure/TakeoutSaaS.Infrastructure/Identity/Persistence/IdentityDbContext.cs

@@ -104,10 +104,12 @@ public sealed class IdentityDbContext(
         builder.Property(x => x.LastLoginAt);
         builder.Property(x => x.MustChangePassword).IsRequired();
         builder.Property(x => x.Avatar).HasColumnType("text");
-        builder.Property(x => x.RowVersion)
-            .IsRowVersion()
-            .IsConcurrencyToken()
-            .HasColumnType("bytea");
+        builder.Ignore(x => x.RowVersion);
+        builder.Property<uint>("xmin")
+            .HasColumnName("xmin")
+            .HasColumnType("xid")
+            .ValueGeneratedOnAddOrUpdate()
+            .IsConcurrencyToken();
         builder.Property(x => x.TenantId).IsRequired();
         ConfigureAuditableEntity(builder);
         ConfigureSoftDeleteEntity(builder);