Serve images without PHP, add the 720 and 1280 steps, trim two hot paths

- Image widths are 480, 720, 960, 1280, 1600 and 2400. A phone needed
  721 pixels and got 960. Existing images receive the new steps from
  a task; stored pages pick them up at render time, so no document is
  rewritten. Mobile backgrounds use 720.
- A variant served once is mirrored to public/media, and a rewrite rule
  lets the web server deliver it from there. var/media stays the source.
- The hero preload follows the image each device really shows.
- The post navigation reads the order and then two posts instead of
  up to 500 documents.

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

src/Ops/Tasks/CleanupTask.php

@@ -2,6 +2,7 @@
 
 namespace App\Ops\Tasks;
 
+use App\Content\MediaMirror;
 use App\Ops\ArchiveUpdate;
 use App\Ops\Scheduler;
 use App\Ops\Updater;
@@ -26,7 +27,7 @@ final class CleanupTask implements Task
     /** So viele Zeilen bleiben in den Protokollen stehen. */
     private const KEEP_LINES = 200;
 
-    public function __construct(private string $projectDir)
+    public function __construct(private string $projectDir, private ?MediaMirror $mirror = null)
     {
     }
 
@@ -57,12 +58,16 @@ final class CleanupTask implements Task
     {
         $limit = time() - self::KEEP_DAYS * 86400;
 
-        return sprintf(
+        $bericht = sprintf(
             '%d Sitzungsdatei(en), %d Update-Ordner entfernt, %d Protokoll(e) gekürzt.',
             $this->sessions($limit),
             $this->updateFolders($limit),
             $this->logs(),
         );
+        // Bildvarianten im öffentlichen Abbild, deren Bild es nicht mehr gibt.
+        $verwaist = $this->mirror?->prune() ?? 0;
+
+        return 0 === $verwaist ? $bericht : $bericht.sprintf(' %d verwaiste Bilddatei(en) aus public/media entfernt.', $verwaist);
     }
 
     /** Sitzungsdateien. Der Garbage Collector von PHP ist auf vielen Hostings abgeschaltet. */