fix(worker): batch_get_tasks accept "number" and "id" in fields filter

batch_get_tasks with fields: ["number", ...] was rejected with "Unknown
field(s)" even though every task DTO always carries id and number. Add
both to KnownDetailFields so they are accepted; BuildDetail already emits
them regardless of the fields filter.

Also add a test verifying fields: ["number", "title"] works and
description is properly excluded.

src/ClaudeDo.Worker/External/BatchMcpTools.cs

@@ -79,7 +79,7 @@ public sealed class BatchMcpTools
 
     private static readonly string[] KnownDetailFields =
     {
-        "listId", "title", "description", "status", "result", "createdBy", "createdAt",
+        "id", "number", "listId", "title", "description", "status", "result", "createdBy", "createdAt",
         "startedAt", "finishedAt", "isMyDay", "sortOrder", "roadblockCount", "roadblockText",
         "failureReason",
     };