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.

src/ClaudeDo.Worker/External/LifecycleMcpTools.cs

@@ -6,6 +6,8 @@ using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
 namespace ClaudeDo.Worker.External;
 
+public sealed record ResetFailedTaskResult(bool Reset, string TaskId);
+
 [McpServerToolType]
 public sealed class LifecycleMcpTools
 {
@@ -18,8 +20,8 @@ public sealed class LifecycleMcpTools
         _reset = reset;
     }
 
-    [McpServerTool, Description("Reset a failed task: discards its worktree and returns it to Idle so it can be run again. Only Failed tasks are accepted.")]
-    public async Task ResetFailedTask(string taskId, CancellationToken cancellationToken)
+    [McpServerTool, Description("Reset a failed task: discards its worktree and returns it to Idle so it can be run again. Only Failed tasks are accepted. Returns { reset: true, taskId } on success.")]
+    public async Task<ResetFailedTaskResult> ResetFailedTask(string taskId, CancellationToken cancellationToken)
     {
         var task = await _tasks.GetByIdAsync(taskId, cancellationToken)
             ?? throw new InvalidOperationException($"Task {taskId} not found.");
@@ -27,5 +29,6 @@ public sealed class LifecycleMcpTools
             throw new InvalidOperationException($"Task {taskId} is {task.Status}, not Failed. Only failed tasks can be reset via this tool.");
 
         await _reset.ResetAsync(taskId, cancellationToken);
+        return new ResetFailedTaskResult(true, taskId);
     }
 }