claudetool: remove knowledge base, focus on about sketch

We should have a more general kb.
Meanwhile, this is important and standalone.
Make it all clearer and sharper.
diff --git a/claudetool/codereview/differential.go b/claudetool/codereview/differential.go
index f7ec670..e3a819a 100644
--- a/claudetool/codereview/differential.go
+++ b/claudetool/codereview/differential.go
@@ -31,7 +31,7 @@
 		Name:        "codereview",
 		Description: `Run an automated code review.`,
 		// If you modify this, update the termui template for prettier rendering.
-		InputSchema: llm.MustSchema(`{"type": "object", "properties": {}}`),
+		InputSchema: llm.EmptySchema(),
 		Run:         r.Run,
 	}
 	return spec