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-dialog.css

@@ -28,3 +28,13 @@
 .media-dialog> .panel-hint{margin-top:20px}
 .media-details>p{font-size:12px}
 @media(max-width:767px){.media-dialog{padding:18px}.media-tools,.media-layout{grid-template-columns:1fr}.media-details{padding:20px 0 0;border-left:0;border-top:1px solid var(--line)}.media-grid{max-height:280px;grid-template-columns:repeat(2,minmax(0,1fr))}.media-footer{align-items:stretch;flex-direction:column}.media-heading{gap:8px}}
+/* PDFs: eine Liste statt eines Rasters - es gibt nichts zu sehen außer dem Titel. */
+.document-dialog{max-width:720px}
+.document-list{display:grid;gap:8px;max-height:360px;overflow:auto;padding:4px}
+.document-card{display:grid;grid-template-columns:auto minmax(0,1fr) auto;align-items:center;gap:12px;border:2px solid var(--line);border-radius:9px;padding:10px 12px;background:white;color:var(--ink);text-align:left}
+.document-card[aria-pressed=true]{border-color:var(--accent);background:#edf4dc}
+.document-card strong{font-size:13px;overflow-wrap:anywhere}
+.document-card span{font-size:11px;color:var(--muted)}
+.document-card .document-badge{font-weight:700;color:#8b2f22;background:#fff0eb;border-radius:5px;padding:4px 6px;letter-spacing:.04em}
+.media-error{color:#8b2f22;background:#fff0eb;padding:12px;border-radius:6px}
+.href-document{margin:6px 0 4px}