Guest control: Cleaned methods involved in fetching/handling

- Moves guest user caching from User class to app container for
  simplicity.
- Updates test to use simpler $this->users->guest() method for
  consistency.
- Streamlined helpers to avoid function overlap for simplicity.
- Extracted user profile dropdown while doing changes.

app/Http/Controller.php

@@ -71,7 +71,7 @@ abstract class Controller extends BaseController
      */
     protected function preventGuestAccess(): void
     {
-        if (!signedInUser()) {
+        if (user()->isGuest()) {
             $this->showPermissionError();
         }
     }