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/ListMcpTools.cs

@@ -7,6 +7,7 @@ using ModelContextProtocol.Server;
 namespace ClaudeDo.Worker.External;
 
 public sealed record ListSummaryDto(string Id, string Name, string? WorkingDir, string DefaultCommitType);
+public sealed record DeleteListResult(bool Deleted, string Id);
 
 [McpServerToolType]
 public sealed class ListMcpTools
@@ -61,13 +62,14 @@ public sealed class ListMcpTools
         return ToDto(entity);
     }
 
-    [McpServerTool, Description("Delete a list and its tasks. Irreversible.")]
-    public async Task DeleteList(string listId, CancellationToken cancellationToken)
+    [McpServerTool, Description("Delete a list and its tasks. Irreversible. Returns { deleted: true, id } on success.")]
+    public async Task<DeleteListResult> DeleteList(string listId, CancellationToken cancellationToken)
     {
         _ = await _lists.GetByIdAsync(listId, cancellationToken)
             ?? throw new InvalidOperationException($"List {listId} not found.");
         await _lists.DeleteAsync(listId, cancellationToken);
         await _broadcaster.ListUpdated(listId);
+        return new DeleteListResult(true, listId);
     }
 
     private static ListSummaryDto ToDto(ListEntity l) =>