feat(worker): accept #123 task numbers as MCP tool input

TaskIdResolver resolves a #123/bare-123 taskId parameter to its GUID
before any lookup, across every External/ MCP tool that takes a task
id, including the batch tools' id arrays (via delegation to the
already-resolving single-entity methods) and update_task's
dependsOnTaskId (empty string still passes through unchanged as the
clear-link sentinel). An unknown number throws a clear error instead
of a silent null. McpToolDocs.TaskNumberHint tells the agent to refer
to tasks as #<number> when reporting to the user, added to the
description of get_task, list_tasks, add_task, update_task_status and
review_task.

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

@@ -205,6 +205,22 @@ public sealed class BatchMcpToolsTests : IDisposable
         Assert.Null(found.TaskFull);
     }
 
+    [Fact]
+    public async Task BatchGetTasks_MixedNumberAndGuidIds_ResolvesBoth()
+    {
+        var listId = await SeedListAsync();
+        var a = await SeedTaskAsync(listId);
+        var b = await SeedTaskAsync(listId);
+        var sut = BuildSut();
+
+        var results = await sut.BatchGetTasks(new[] { $"#{a.Number}", b.Id }, cancellationToken: CancellationToken.None);
+
+        Assert.True(results[0].Found);
+        Assert.Equal(a.Id, results[0].Task!.Id);
+        Assert.True(results[1].Found);
+        Assert.Equal(b.Id, results[1].Task!.Id);
+    }
+
     [Fact]
     public async Task BatchGetTasks_IncludeDescriptionTrue_ReturnsTaskFull()
     {