feat: add videodb media index with Docker stack

- Add videodb PHP/MySQL media collection manager (Blu-ray, DVD, CD)
- Dockerfile: PHP 8.1 + Apache with GD/mysqli/exif extensions
- docker-compose.yml: app on port 6761 + MySQL 8.0 with health checks
- docker-entrypoint.sh: auto-generates config.inc.php from env vars,
  waits for MySQL, initializes DB schema idempotently
- init-db.php: CLI schema installer using app's own prefix_query() logic
- Persistent volumes for DB, cache, and cover images

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

videodb/vendor/symfony/polyfill-php70/bootstrap.php

@@ -0,0 +1,30 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+use Symfony\Polyfill\Php70 as p;
+
+if (PHP_VERSION_ID >= 70000) {
+    return;
+}
+
+if (!defined('PHP_INT_MIN')) {
+    define('PHP_INT_MIN', ~PHP_INT_MAX);
+}
+
+if (!function_exists('intdiv')) {
+    function intdiv($num1, $num2) { return p\Php70::intdiv($num1, $num2); }
+}
+if (!function_exists('preg_replace_callback_array')) {
+    function preg_replace_callback_array(array $pattern, $subject, $limit = -1, &$count = 0, $flags = null) { return p\Php70::preg_replace_callback_array($pattern, $subject, $limit, $count); }
+}
+if (!function_exists('error_clear_last')) {
+    function error_clear_last() { return p\Php70::error_clear_last(); }
+}