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>

templates/favicon.html.twig

@@ -1,10 +1,12 @@
 {# Das Symbol der Website. Eigenes Bild aus den Einstellungen, sonst das mitgelieferte Zeichen.
-   Die Kennung hängt als Version am Verweis, damit ein Wechsel im Browser auch ankommt. #}
+   Die Kennung hängt als Version am Verweis, damit ein Wechsel im Browser auch ankommt.
+   Das 192er ist für die Google-Suche: sie nimmt nur Vielfache von 48 px. #}
 {% set site = siteSettings.load() %}
 {% set favicon = site.faviconMediaId|default('') %}
 {% set version = site.faviconVersion|default('') ?: favicon|slice(0, 8) %}
 {% if favicon %}
     <link rel="icon" href="/favicon.png?v={{ version }}" type="image/png" sizes="32x32">
+    <link rel="icon" href="/favicon-192.png?v={{ version }}" type="image/png" sizes="192x192">
     <link rel="apple-touch-icon" href="/apple-touch-icon.png?v={{ version }}">
 {% else %}
     <link rel="icon" href="/favicon.svg" type="image/svg+xml">