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>

scripts/reset-kantarci-immobilien.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+# Wirft die KANTARCI-Installation weg und baut sie neu auf. Nur fuer den Aufbau gedacht.
+set -e
+root="C:/Django Project/KantSites"
+php="${PHP_BINARY:-C:/php84/php.exe}"
+export DATABASE_URL="sqlite:///$root/var/kantarci-immobilien.db"
+export MEDIA_DIRECTORY="$root/var/kantarci-immobilien-media"
+rm -f "$root/var/kantarci-immobilien.db"
+rm -rf "$root/var/kantarci-immobilien-media"
+"$php" vendor/bin/doctrine-migrations migrate --no-interaction -q
+assets="${1:-$root/var/kantarci-immobilien-assets}"
+# Logo, Hausmotiv und Symbol sind Zuschnitte aus dem gelieferten Banner, die Bildkarten
+# der Mietanfrage zeichnet Chromium (Playwright).
+"$php" scripts/build-kantarci-assets.php "$assets/kantarci-banner.jpeg" "$assets"
+node scripts/build-kantarci-options.mjs "$assets/options"
+# Die Vorlage nutzt Arial und Georgia; es gibt keine Schrift zu holen.
+"$php" -d memory_limit=512M scripts/seed-kantarci-immobilien.php "$assets"