loop: add knowledge_base tool for on-demand information

The knowledge_base tool provides a way for agents to access specialized information
when needed. Initial topics include:

- sketch: how to use Sketch, including SSH, secrets, and file management
- go_iterators: information about Go's iterator feature added in Go 1.22

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/experiment/experiment.go b/experiment/experiment.go
index 60bc0b5..ab2a2f2 100644
--- a/experiment/experiment.go
+++ b/experiment/experiment.go
@@ -36,6 +36,10 @@
 			Name:        "memory",
 			Description: "Enable memory subsystem (dear_llm.md)",
 		},
+		{
+			Name:        "kb",
+			Description: "Enable knowledge_base tool",
+		},
 	}
 	byName = map[string]*Experiment{}
 )