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/ExternalMcpToolSchemaTests.cs

@@ -1,3 +1,4 @@
+using System.ComponentModel;
 using System.Reflection;
 using ClaudeDo.Worker.External;
 using Microsoft.Extensions.AI;
@@ -71,4 +72,16 @@ public sealed class ExternalMcpToolSchemaTests
         // (e.g. namespace/attribute mismatch) and the schema test above would pass vacuously.
         Assert.True(ExternalToolMethods().Count() > 20);
     }
+
+    [Fact]
+    public void AtLeastOneTaskIdTool_DescriptionCarriesTaskNumberHint()
+    {
+        // The whole point of task numbers: without this clause the agent never learns to speak
+        // #<number> to the user, even though every DTO already carries it.
+        var hasHint = ExternalToolMethods()
+            .Select(m => m.GetCustomAttribute<DescriptionAttribute>()?.Description ?? "")
+            .Any(d => d.Contains(McpToolDocs.TaskNumberHint.Trim(), StringComparison.Ordinal));
+
+        Assert.True(hasHint, "No external tool description carries McpToolDocs.TaskNumberHint.");
+    }
 }