feat(tasks): persist task deadlines

TaskTracker.Tests/WorkTaskDeadlineTests.cs

@@ -0,0 +1,16 @@
+using TaskTracker.Core.Entities;
+using Xunit;
+
+namespace TaskTracker.Tests;
+
+public class WorkTaskDeadlineTests
+{
+    [Fact]
+    public void WorkTask_preserves_an_explicit_deadline_offset()
+    {
+        var dueAt = DateTimeOffset.Parse("2026-08-14T11:00:00-04:00");
+        var task = new WorkTask { DueAt = dueAt };
+
+        Assert.Equal(dueAt, task.DueAt);
+    }
+}