chore(worker): external MCP tools return explicit results instead of empty responses

set_task_config/set_list_config now echo which fields were set vs cleared, get_list_config/get_task_config return an explicit found=false instead of null, and delete_list/run_task_now/reset_failed_task/remove_task_attachment return a confirmation record — matching the found/ok convention already used by batch_get_tasks and get_task_log.

tests/ClaudeDo.Worker.Tests/External/LifecycleMcpToolsTests.cs

@@ -64,8 +64,10 @@ public sealed class LifecycleMcpToolsTests : IDisposable
         var task = await SeedTaskAsync(TaskStatus.Failed);
         var sut = BuildSut();
 
-        await sut.ResetFailedTask(task.Id, CancellationToken.None);
+        var result = await sut.ResetFailedTask(task.Id, CancellationToken.None);
 
+        Assert.True(result.Reset);
+        Assert.Equal(task.Id, result.TaskId);
         var loaded = await _tasks.GetByIdAsync(task.Id);
         Assert.Equal(TaskStatus.Idle, loaded!.Status);
     }