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/termui/termui.go b/termui/termui.go
index 7e4def9..1575473 100644
--- a/termui/termui.go
+++ b/termui/termui.go
@@ -43,6 +43,8 @@
 🏷️  {{.input.title}}
 {{else if eq .msg.ToolName "precommit" -}}
 🌱 git branch: sketch/{{.input.branch_name}}
+{{else if eq .msg.ToolName "knowledge_base" -}}
+📚 Knowledge: {{.input.topic}}
 {{else if eq .msg.ToolName "str_replace_editor" -}}
  ✏️  {{.input.file_path -}}
 {{else if eq .msg.ToolName "codereview" -}}