File manager
A two-pane file explorer whose preview adapts to each file type. The left pane is a tree; the right pane swaps in the right viewer for the file you open — CodeView for source, MarkdownView for docs, JsonView for data.
Each viewer is a drop-in widget with selection, scrolling, and copy already handled, so “the preview matches the file” comes down to a switch in build().
Try it: use the arrows to move to a file, then press Enter or click it to open its preview.