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",
     };

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

@@ -324,6 +324,26 @@ public sealed class BatchMcpToolsTests : IDisposable
         Assert.Contains("notAField", ex.Message);
     }
 
+    [Fact]
+    public async Task BatchGetTasks_NumberAndIdFields_AcceptedAndReturned()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId);
+        task.Description = "full description not requested";
+        await _tasks.UpdateAsync(task);
+        var sut = BuildSut();
+
+        var results = await sut.BatchGetTasks(
+            new[] { task.Id }, includeDescription: true, fields: new[] { "number", "title" },
+            cancellationToken: CancellationToken.None);
+
+        var found = results.Single(r => r.Id == task.Id).TaskFull!;
+        Assert.Equal(task.Number, found.Number);
+        Assert.Equal(task.Id, found.Id);
+        Assert.Equal(task.Title, found.Title);
+        Assert.Null(found.Description); // Not requested
+    }
+
     [Fact]
     public async Task BatchGetTasks_RoadblockTextField_ExtractsTailOfResult_WithoutFullResult()
     {