fix(db): register legacy task migrations

backend/Data/Migrations/20260618233001_AddTaskDueDate.cs

@@ -1,28 +1,34 @@
+using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Migrations;
+using Nexus.Api.Data;
 
 #nullable disable
 
 namespace Nexus.Api.Migrations
 {
     /// <inheritdoc />
+    [DbContext(typeof(NexusDbContext))]
+    [Migration("20260618233001_AddTaskDueDate")]
     public partial class AddTaskDueDate : Migration
     {
         /// <inheritdoc />
         protected override void Up(MigrationBuilder migrationBuilder)
         {
-            migrationBuilder.AddColumn<DateTimeOffset>(
-                name: "DueDate",
-                table: "Tasks",
-                type: "timestamp with time zone",
-                nullable: true);
+            migrationBuilder.Sql(
+                """
+                ALTER TABLE "Tasks"
+                    ADD COLUMN IF NOT EXISTS "DueDate" timestamp with time zone;
+                """);
         }
 
         /// <inheritdoc />
         protected override void Down(MigrationBuilder migrationBuilder)
         {
-            migrationBuilder.DropColumn(
-                name: "DueDate",
-                table: "Tasks");
+            migrationBuilder.Sql(
+                """
+                ALTER TABLE "Tasks"
+                    DROP COLUMN IF EXISTS "DueDate";
+                """);
         }
     }
 }