Breadcrumb Navigation
Build a file explorer with breadcrumb navigation. Click folders to navigate in, click breadcrumb segments to navigate back. The folder tree and UI shell are ready — wire up the navigation logic.
Track the current path as an array of FolderItem[]. Navigating into a folder pushes it onto the array. Clicking a breadcrumb slices the array to that index. The last item is always the current folder. Check the TODOs in the code.