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/james-heinrich/phpthumb/index.php

@@ -0,0 +1,10 @@
+<?php
+if (!file_exists('phpThumb.config.php')) {
+	if (file_exists('phpThumb.config.php.default')) {
+		echo 'WARNING! "phpThumb.config.php.default" MUST be renamed to "phpThumb.config.php"';
+	} else {
+		echo 'WARNING! "phpThumb.config.php" should exist but does not';
+	}
+	exit;
+}
+header('Location: ./demo/');