Issue: Migrate deprecated state hook and enhance CodeHighlighter header customization

Issue: Migrate deprecated state hook and enhance CodeHighlighter header customization: a task in LegoFlow-SWE (Harbor dataset). Observed behavior: Components using useMergedState appear to work in most cases, but the deprecation notice and potential misalignment with the newer utility need to be…

The task

**Observed behavior:** Components using `useMergedState` appear to work in most cases, but the deprecation notice and potential misalignment with the newer utility need to be addressed.

Part of Lego-X/LegoFlow-SWE.