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

public/.htaccess

@@ -44,7 +44,13 @@
     RewriteCond %{REQUEST_FILENAME} -f
     RewriteRule ^assets/.*$ - [L]
     
-    # Block direct access to all content files
+    # Allow access to content assets
+    RewriteRule ^content/assets/.*$ - [L]
+    
+    # Serve files from content/-assets/ via index.php
+    RewriteRule ^-assets/.*$ index.php [L]
+    
+    # Block direct access to all other content files
     RewriteRule ^content/.*$ - [F,L]
 </IfModule>