Show the own site icon to Google under every address, and the KANTARCI landing page

- Google kept showing the KantSites K for Elektro Bernhard after the site
  icon was changed. The own icon only existed at 32 and 180 px, and Google
  takes multiples of 48 only; /favicon.svg was a file in public/, so the web
  server always delivered the bundled K.
- The icon is now also cut at 48 and 192 px. The head links /favicon-192.png,
  /favicon.ico serves the 48 px PNG, and /favicon.svg is answered by the
  application: the bundled mark without an own icon (now in
  public/assets/favicon.svg), otherwise a 302 to the 192 px PNG. Sites that
  set their icon earlier get the new sizes on first request. A removed icon
  no longer counts even though its files remain.
- The archive update only adds files to public/, so it now deletes the old
  public/favicon.svg explicitly.
- Seventh local reference site: the KANTARCI Immobilien landing page with a
  three-step rental request, own database, seed and reset scripts.

Tests: 582 PHPUnit on PHP 8.2 and 8.4, 35 node, test:editor and
test:browser green (test:browser reports only the known editor colour
contrast on /grundlagen).

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

src/Content/MediaLibrary.php

@@ -215,8 +215,12 @@ final class MediaLibrary
         return [...$data, 'id' => $id, 'version' => $data['version'] + 1];
     }
 
-    /** Die Größen, die ein Favicon braucht: der Reiter im Browser und das Symbol auf dem Startbildschirm. */
-    public const FAVICON_SIZES = [32, 180];
+    /**
+     * Die Größen, die ein Favicon braucht: 32 für den Reiter im Browser, 180 für den
+     * Startbildschirm, 48 und 192 für die Google-Suche - Google nimmt nur Vielfache von 48 und
+     * behielt sonst das zuerst gefundene Symbol, bei Elektro Bernhard das mitgelieferte K.
+     */
+    public const FAVICON_SIZES = [32, 48, 180, 192];
 
     /**
      * Erzeugt aus einem Bild der Mediathek die Symboldateien der Website.