refactor(background-agent): simplify loop detector null guard

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/background-agent/loop-detector.ts

@@ -62,7 +62,7 @@ export function recordToolCall(
 }
 
 function sortObject(obj: unknown): unknown {
-  if (obj === null || obj === undefined) return obj
+  if (obj == null) return obj
   if (typeof obj !== "object") return obj
   if (Array.isArray(obj)) return obj.map(sortObject)