{# Reusable image picker element. Renders a thumbnail (drag-and-drop + live preview), a compact one-line control row [ select | delete | upload ], a recommended-size hint and a progress area. Image changes apply instantly (see the generic `.image-picker` handler in the consuming page's JS) -- there is no per-image Apply button. Set a `picker` dict immediately before including this file. Keys: id base id; derives #{id}_thumb / _select / _file / _progress label heading text options list of existing filenames for the dropdown selected currently-selected filename (equal to default_value = stock) default_label dropdown label for the stock/default entry default_value select value meaning "use stock" ('' for logos/embed, 'login_1.jpg' for background). A synthetic default