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/MQTTTracker/MQTTTracker.php

@@ -31,6 +31,7 @@ class MQTTTracker
         $configFile = __DIR__ . '/config.json';
         $this->config = [
             'enabled' => true,
+            'viewable' => false,
             'broker_host' => 'localhost',
             'broker_port' => 1883,
             'client_id' => 'codepress_cms',