Back up unsaved editor work locally, structure the settings, fix archive accessibility

- The editor keeps unsaved changes in the browser and offers them
  after a crash, a closed tab or an expired session. No timed save on
  the server: every save is a full revision.
- The save status stays visible in narrow windows.
- Settings get a sticky section bar, two folded groups and a save bar
  that stays in view.
- The admin post list fetches terms and images once, not per post.
- Archive post titles are second-level headings, the archive head
  keeps full text contrast, the skip link sits above a sticky header,
  a linked image without alternative text names its link.
- The editor check starts through the dev router like the others.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

src/Content/MediaLibrary.php

@@ -130,7 +130,8 @@ final class MediaLibrary
             'SELECT * FROM media WHERE id IN ('.implode(',', array_fill(0, count($ids), '?')).')',
             $ids,
         ) as $row) {
-            $found[$row['id']] = $this->present($row);
+            // Auch für find(): Wer die Bilder einer Liste vorab holt, erspart jede Einzelabfrage danach.
+            $found[$row['id']] = $this->gemerkt[$row['id']] = $this->present($row);
         }
 
         return $found;