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/help.php

@@ -0,0 +1,44 @@
+<?php
+/**
+ * Help Page
+ *
+ * Browses the manual
+ *
+ * @package videoDB
+ * @author  Andreas Gohr <a.gohr@web.de>
+ * @version $Id: help.php,v 1.10 2004/09/20 15:15:41 andig2 Exp $
+ */
+
+require_once './core/functions.php';
+
+function _replace_anchors_callback($matches)
+{
+	if (!preg_match('=^https?://=',$matches[2])) 
+    {
+		$matches[2] = 'help.php?page='.$matches[2];
+	}
+	return $matches[1].$matches[2].$matches[3];
+}
+
+/**
+ * input
+ */
+$page = req_string('page');
+
+if (empty($page) || !preg_match('#^([a-z]{3,20})\.html$#', $page, $match)) $page = 'index.html';
+$page = 'doc/manual/' . $page;
+if (!file_exists($page)) $page = 'doc/manual/index.html';
+
+$html = file_get_contents($page);
+$html = preg_replace_callback("/(<a\s+.*?href\s*=\s*\")(.*?)(\".*?>)/is", '_replace_anchors_callback', $html);
+preg_match('=<body.*?>(.*)</body>=is',$html,$matches);
+$html = $matches[1];
+
+// prepare templates
+tpl_page();
+
+$smarty->assign('helptext', $html);
+
+// display templates
+tpl_display('help.tpl');
+