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>

public/assets/media-drop.js

@@ -1,5 +1,5 @@
 /**
- * Dragging images onto the upload field, and saying which files are about to go up.
+ * Dragging images and PDFs onto the upload field, and saying which files are about to go up.
  *
  * Everything here is an addition. Without this script the field is still a file input with a
  * label: clicking it opens the file picker and the form submits the same way. The script never
@@ -9,19 +9,19 @@ const zone = document.querySelector('[data-dropzone]');
 const input = zone?.querySelector('input[type="file"]');
 const chosen = document.querySelector('[data-chosen]');
 if (zone && input && chosen) {
-  const ACCEPTED = ['image/jpeg', 'image/png', 'image/webp'];
+  const ACCEPTED = ['image/jpeg', 'image/png', 'image/webp', 'application/pdf'];
 
   const describe = (files, ignored = 0) => {
     if (!files.length) {
       chosen.textContent = ignored
-        ? `Keine Bilddatei dabei. ${ignored} Datei(en) übersprungen – erlaubt sind JPEG, PNG und WebP.`
+        ? `Keine passende Datei dabei. ${ignored} Datei(en) übersprungen – erlaubt sind JPEG, PNG, WebP und PDF.`
         : 'Noch keine Datei gewählt.';
       return;
     }
     const names = [...files].map(file => file.name).join(', ');
     const size = [...files].reduce((total, file) => total + file.size, 0);
     chosen.textContent = `${files.length} Datei(en) gewählt (${(size / 1048576).toFixed(1)} MB): ${names}`
-      + (ignored ? ` · ${ignored} Datei(en) übersprungen, erlaubt sind JPEG, PNG und WebP.` : '');
+      + (ignored ? ` · ${ignored} Datei(en) übersprungen, erlaubt sind JPEG, PNG, WebP und PDF.` : '');
   };
 
   input.addEventListener('change', () => describe(input.files));