Upload PDFs to the library, link them from any link target, show them in a viewer

PDFs go through the same upload field as images, are checked by their content and kept
unchanged in their own table. Every link field can pick one, and a page that links a PDF
opens it in a dialog with the browser's own viewer; touch devices and browsers without a
viewer get a new tab instead.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

templates/page.html.twig

@@ -62,7 +62,7 @@
     {% if needsSlider|default(false) %}<script type="module" src="/assets/slider.js?v={{ kant_version() }}"></script>{% endif %}
     {% if needsMotion|default(false) %}<script type="module" src="/assets/motion.js?v={{ kant_version() }}"></script>{% endif %}
     {% if needsScrolled|default(false) %}<script type="module" src="/assets/scrolled.js?v={{ kant_version() }}"></script>{% endif %}
-    {% if needsZoom|default(false) %}<script src="/assets/lightbox.js?v={{ kant_version() }}" defer></script>{% endif %}
+    {% if needsZoom|default(false) or needsDocument|default(false) %}<script src="/assets/lightbox.js?v={{ kant_version() }}" defer></script>{% endif %}
     {% if not editing|default(false) %}{% for src in pluginScripts|default([]) %}<script src="{{ src }}" defer></script>{% endfor %}{% endif %}
     {# Own scripts of this page, as a file. Never rendered in the editor preview: the preview must
        show the layout, not run code that could change the page under the editor's hands. #}