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

tests/TestSchema.php

@@ -24,6 +24,7 @@ use DoctrineMigrations\Version20260916000100;
 use DoctrineMigrations\Version20260917000100;
 use DoctrineMigrations\Version20261009000100;
 use DoctrineMigrations\Version20261012000100;
+use DoctrineMigrations\Version20261104000100;
 use Psr\Log\NullLogger;
 
 /**
@@ -59,6 +60,7 @@ final class TestSchema
             Version20260917000100::class,
             Version20261009000100::class,
             Version20261012000100::class,
+            Version20261104000100::class,
         ] as $migration) {
             (new $migration($db, new NullLogger()))->up($schema);
         }