feat(storage): support deleting backends and improve admin UI

- Implement storage backend deletion, which automatically resets default storage settings and user-specific overrides when a backend is removed.
- Add unit tests covering the delete action and its cleanup side effects.
- Improve admin UI responsiveness, fixing table scrolling, flex wrapping, and text truncation for long storage backend names.
- Update security documentation to clarify trusted proxy configurations and explain how trusted proxies are protected from automatic bans.

backend/static/js/05-theme.js

@@ -11,7 +11,7 @@
  */
 (function () {
   var STORAGE_KEY = "warpbox-theme";
-  var THEMES = ["revamp", "classic", "retro"];
+  var THEMES = ["revamp", "classic", "retro", "gruvbox", "cyberpunk"];
 
   function stored() {
     try {