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/core/session.php

@@ -0,0 +1,69 @@
+<?php
+/**
+ * Session functions
+ *
+ * Moved all session functions into one file, 
+ * include this where session starting might be required
+ *
+ * @package Core
+ * @author  Andreas Goetz <cpuidle@gmx.de>
+ * @version $Id: session.php,v 1.13 2008/02/28 20:01:17 andig2 Exp $
+ */
+
+// start session
+session_start();
+
+/**
+ * Get session value or specified default
+ */
+function session_get($varname, $default=null)
+{
+    if (isset($_SESSION['vdb'][$varname]))
+    {
+        return $_SESSION['vdb'][$varname];
+    }
+    return $default;
+}    
+
+/**
+ * Set session value or specified default
+ */
+function session_set($varname, $value)
+{
+    $_SESSION['vdb'][$varname] = $value;
+}    
+
+/**
+ * Upsert session value with current value of global variable or specified default
+ */
+function session_default($varname, $default=null)
+{
+    global $$varname;
+
+    if (!isset($$varname))
+    {
+        $$varname = (isset($_SESSION['vdb'][$varname])) ? $_SESSION['vdb'][$varname] : $default;
+    }
+    $_SESSION['vdb'][$varname] = $$varname;
+}    
+
+/**
+ * get session_default for owner
+ * 
+ * basically this only executes the extra query when the global $owner is not set and also
+ * not available in session data. only then we need the hasAny check. if the global is set
+ * or the global is not set but the session is then session_default() will fix both those
+ * cases. put into a single function because it gets called from multiple files.
+ */
+function session_default_owner()
+{
+    global $owner, $lang;
+    if (!isset($owner) && !isset($_SESSION['vdb']['owner'])) {
+        $hasAny = runSQL('SELECT COUNT(*) AS num FROM '.TBL_DATA.' WHERE '.TBL_DATA.'.owner_id = ' . get_current_user_id());
+        $hasAny = ($hasAny && isset($hasAny[0]['num']) && $hasAny[0]['num'] > 0);
+        $default = ($hasAny ? get_username(get_current_user_id()) : $lang['filter_any']);
+        return session_default('owner', $default);
+    }
+    return session_default('owner');
+}
+