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/README.md

@@ -0,0 +1,28 @@
+Symfony Polyfill / Php70
+========================
+
+This component provides features unavailable in releases prior to PHP 7.0:
+
+- [`intdiv`](https://php.net/intdiv)
+- [`preg_replace_callback_array`](https://php.net/preg_replace_callback_array)
+- [`error_clear_last`](https://php.net/error_clear_last)
+- `random_bytes` and `random_int` (from [paragonie/random_compat](https://github.com/paragonie/random_compat))
+- [`*Error` throwable classes](https://php.net/Error)
+- [`PHP_INT_MIN`](https://php.net/reserved.constants#constant.php-int-min)
+- `SessionUpdateTimestampHandlerInterface`
+
+More information can be found in the
+[main Polyfill README](https://github.com/symfony/polyfill/blob/master/README.md).
+
+Compatibility notes
+===================
+
+To write portable code between PHP5 and PHP7, some care must be taken:
+- `\*Error` exceptions must be caught before `\Exception`;
+- after calling `error_clear_last()`, the result of `$e = error_get_last()` must be
+  verified using `isset($e['message'][0])` instead of `null !== $e`.
+
+License
+=======
+
+This library is released under the [MIT license](LICENSE).