Add an own-HTML block, and build the DEEG offers page on the embed block

Umut asked for a block that takes custom HTML, and for an iframe on a new
DEEG offers page. Only one of those was missing.

New core block "Eigenes HTML" (document schema v24): one property, the
markup, up to 20.000 characters, written to the page unchanged. Changing it
is reserved for administrators and compared against what is stored - on
saving, on saving an area, and on restoring an older revision - exactly like
an own script. <script> and <iframe> are refused with the way to the right
place instead of being swallowed by the content security policy: scripts
belong in the script field, frames in the "Externer Inhalt" block, because
only that one asks for consent and puts the host into frame-src (ADR 106).

DEEG: /angebote existed as a draft with placeholder text. It is now built
like the legal pages - small caps line, large light heading, lead on the
tinted band - with the IS24 result list below it and a line pointing to the
portal and to the contact form. Navigation and the offers band on the home
page point there. The consent question is switched on, so the frame loads
only after the visitor agrees, and both the banner and the placeholder carry
the site's own shapes and colours.

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

src/Content/DocumentValidator.php

@@ -38,8 +38,9 @@ final class DocumentValidator
     public const V15_TYPES = ['icon', 'progress', 'slider'];
     /** Schema v23: die sozialen Profile aus den Einstellungen, als Symbolreihe an jeder Stelle. */
     public const V23_TYPES = ['social'];
+    public const V24_TYPES = ['html'];
     /** Die aktuelle Fassung des Dokumentschemas - dieselbe Zahl wie SCHEMA_VERSION in editor-model.js. */
-    public const SCHEMA_VERSION = 23;
+    public const SCHEMA_VERSION = 24;
 
     /**
      * @param bool $requireHeading A page needs exactly one main heading. A header, a footer or a
@@ -98,7 +99,7 @@ final class DocumentValidator
         // page: a deactivated plugin must never make stored content unreadable. Nothing from
         // props is rendered for such a block, so unvalidated values never reach the output.
         $plugin = $schemaVersion >= 4 && is_string($type) && 1 === preg_match('/^[a-z][a-z0-9]{1,30}\.[a-z][a-z0-9-]{1,40}$/D', $type);
-        $this->require(in_array($type, ['section', 'row', 'column', 'heading', 'text', 'image', 'button'], true) || ($schemaVersion >= 3 && 'gallery' === $type) || ($schemaVersion >= 5 && 'postlist' === $type) || ($schemaVersion >= 6 && in_array($type, self::V6_TYPES, true)) || ($schemaVersion >= 7 && in_array($type, self::V7_TYPES, true)) || ($schemaVersion >= 8 && in_array($type, self::V8_TYPES, true)) || ($schemaVersion >= 9 && in_array($type, self::V9_TYPES, true)) || ($schemaVersion >= 11 && in_array($type, self::V11_TYPES, true)) || ($schemaVersion >= 14 && in_array($type, self::V14_TYPES, true)) || ($schemaVersion >= 15 && in_array($type, self::V15_TYPES, true)) || ($schemaVersion >= 18 && in_array($type, self::V18_TYPES, true)) || ($schemaVersion >= 19 && in_array($type, self::V19_TYPES, true)) || ($schemaVersion >= 23 && in_array($type, self::V23_TYPES, true)) || $plugin, 'Unknown block type. Preserve source until its plugin is available.');
+        $this->require(in_array($type, ['section', 'row', 'column', 'heading', 'text', 'image', 'button'], true) || ($schemaVersion >= 3 && 'gallery' === $type) || ($schemaVersion >= 5 && 'postlist' === $type) || ($schemaVersion >= 6 && in_array($type, self::V6_TYPES, true)) || ($schemaVersion >= 7 && in_array($type, self::V7_TYPES, true)) || ($schemaVersion >= 8 && in_array($type, self::V8_TYPES, true)) || ($schemaVersion >= 9 && in_array($type, self::V9_TYPES, true)) || ($schemaVersion >= 11 && in_array($type, self::V11_TYPES, true)) || ($schemaVersion >= 14 && in_array($type, self::V14_TYPES, true)) || ($schemaVersion >= 15 && in_array($type, self::V15_TYPES, true)) || ($schemaVersion >= 18 && in_array($type, self::V18_TYPES, true)) || ($schemaVersion >= 19 && in_array($type, self::V19_TYPES, true)) || ($schemaVersion >= 23 && in_array($type, self::V23_TYPES, true)) || ($schemaVersion >= 24 && in_array($type, self::V24_TYPES, true)) || $plugin, 'Unknown block type. Preserve source until its plugin is available.');
         // An accordion entry only ever renders inside an accordion; at the top level or anywhere
         // else it would produce a details element without its group.
         $this->require('accordionitem' !== $type || 'accordion' === $parentType, 'An accordion entry belongs into an accordion.');
@@ -389,6 +390,14 @@ final class DocumentValidator
             $this->require(null === parse_url($url, PHP_URL_PORT) && null === parse_url($url, PHP_URL_USER), 'Die Adresse darf keinen Port und keine Zugangsdaten enthalten.');
             $this->require(is_int($props['height'] ?? null) && $props['height'] >= 150 && $props['height'] <= 1200, 'Die Höhe liegt zwischen 150 und 1200 Pixeln.');
         }
+        if ('html' === $type) {
+            // Eigenes HTML geht unveraendert auf die Seite. Geprueft wird es hier, damit ein
+            // unbrauchbarer Wert beim Speichern eine Meldung bekommt statt beim Ausliefern
+            // stillschweigend zu verschwinden. Wer es setzen darf, ist eine Frage der Rolle und
+            // wird im Controller beantwortet - wie beim eigenen Skript.
+            $this->require(is_string($props['html'] ?? null), 'Eigenes HTML ist Text.');
+            $this->code->checkHtml($props['html']);
+        }
         if ('form' === $type) {
             // Only the address is content. Fields, recipient and consent text stay in the database,
             // so a stored document can never redirect a submission or change what is asked.