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/images/flags/README

@@ -0,0 +1,14 @@
+If you want to add a new language just put a flag image in this directory.
+
+I got all my flags from www.blueflash.de - Unfortunately the images are no
+longer available there but you can still get them from the Webarchive at:
+http://web.archive.org/web/20020205113643/www.blueflash.de/flaggen/landlist.html
+
+Please email videodb-devel@lists.sf.net if you want your flag to be included in 
+the standard distribution.
+
+Note:
+
+To limit the number of flags displayed in the options dialog, a number of flags 
+has been moved into the additional folder. To use these flags, they must be
+copied to the images/flags folder.