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-intl-idn/README.md

@@ -0,0 +1,12 @@
+Symfony Polyfill / Intl: Idn
+============================
+
+This component provides [`idn_to_ascii`](https://php.net/idn-to-ascii) and [`idn_to_utf8`](https://php.net/idn-to-utf8) functions to users who run php versions without the [Intl](https://php.net/intl) extension.
+
+More information can be found in the
+[main Polyfill README](https://github.com/symfony/polyfill/blob/master/README.md).
+
+License
+=======
+
+This library is released under the [MIT license](LICENSE).