Media browser: recursive scan entire content/ tree, /-media/ URL prefix, editor change detection fix

- handleMediaList() now scans content/ recursively for all media files
- URLs use /-media/ prefix mapping directly to content/ (no special cases)
- index.php: added /-media/ route, kept /-assets/ for backward compat
- editor-toolbar.js: fixed editor.on('change') placement (was inside switchMode)
- content-edit.php and content-new.php: back-btn unsaved-changes detection
- Removed unused __editorCleanup global

plugins/test/test.php

@@ -0,0 +1,35 @@
+<?php
+
+class test
+{
+    private ?CMSAPI $api = null;
+    private array $config;
+
+    public function __construct()
+    {
+        $this->config = [
+            'title' => 'Dit is een test plugin',
+            'viewable' => true,
+        ];
+    }
+
+    public function setAPI(CMSAPI $api): void
+    {
+        $this->api = $api;
+    }
+
+    public function getSidebarContent(): string
+    {
+        return 'Hallo';
+    }
+
+    public function getConfig(): array
+    {
+        return $this->config;
+    }
+
+    public function setConfig(array $config): void
+    {
+        $this->config = array_merge($this->config, $config);
+    }
+}