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/AttachmentMcpTools.cs

@@ -10,6 +10,7 @@ using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 namespace ClaudeDo.Worker.External;
 
 public sealed record AttachmentDto(string FileName, long ByteSize, DateTime CreatedAt);
+public sealed record RemoveAttachmentResult(bool Removed, string TaskId, string FileName);
 
 [McpServerToolType]
 public sealed class AttachmentMcpTools
@@ -103,8 +104,8 @@ public sealed class AttachmentMcpTools
 
     [McpServerTool, Description(
         "Remove a single attachment from a task. Deletes both the file on disk and the database record. " +
-        "Refuses if the task is currently Running — cancel it first.")]
-    public async Task RemoveTaskAttachment(
+        "Refuses if the task is currently Running — cancel it first. Returns { removed: true, taskId, fileName } on success.")]
+    public async Task<RemoveAttachmentResult> RemoveTaskAttachment(
         string taskId, string fileName, CancellationToken ct = default)
     {
         var task = await _tasks.GetByIdAsync(taskId, ct)
@@ -115,5 +116,6 @@ public sealed class AttachmentMcpTools
         _store.DeleteFile(taskId, fileName);
         await _attachments.DeleteAsync(taskId, fileName, ct);
         await _broadcaster.TaskUpdated(taskId);
+        return new RemoveAttachmentResult(true, taskId, fileName);
     }
 }