W5 companion widget. ProjectExplorer is data-agnostic over a
ProjectDataSource trait: a tree view with expandable folders and
double-click-to-open, an icon grid with thumbnails (img/placeholder
swatch), a view switcher, and file-drop import via on_drop (platform
FileDrop becomes an internal drag), emitting OpenRequested /
FileDropRequested / ViewChanged requests. flatten_tree (pure) is
unit-tested; examples/project_explorer.rs demos a mock project. 89 widget
tests pass.
Mike-Solar
63dbc64a32