Add videos: library, block and section background

Videos join the media library as their own table (schema v28), with a
video block and a looping background on sections. video.js starts loops
only while visible, offers a pause button and leaves the still image for
reduced motion and data saving.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PWYm8kjAWmZaB2QB2xuBhU

migrations/Version20261104000100.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20261104000100 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Videos in der Mediathek: fuer den Video-Baustein und den Hintergrund einer Sektion.';
+    }
+
+    public function isTransactional(): bool
+    {
+        return false;
+    }
+
+    public function up(Schema $schema): void
+    {
+        // Eine eigene Tabelle wie bei den Dokumenten: jede Stelle, die ein Bild sucht, erwartet
+        // Varianten mit Breite und Hoehe.
+        $video = $schema->createTable('video');
+        $video->addColumn('id', 'string', ['length' => 32]);
+        $video->addColumn('title', 'string', ['length' => 160]);
+        $video->addColumn('mime', 'string', ['length' => 16]);
+        $video->addColumn('bytes', 'integer');
+        $video->addColumn('archived', 'boolean', ['default' => false]);
+        $video->addColumn('version', 'integer', ['default' => 1]);
+        $video->addColumn('created_at', 'datetime_immutable');
+        $video->setPrimaryKey(['id']);
+    }
+
+    public function down(Schema $schema): void
+    {
+        $schema->dropTable('video');
+    }
+}