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/Settings/SettingService.php

@@ -47,7 +47,7 @@ class SettingService
             $default = config('setting-defaults.user.' . $key, false);
         }
 
-        if ($user->isDefault()) {
+        if ($user->isGuest()) {
             return $this->getFromSession($key, $default);
         }
 
@@ -206,7 +206,7 @@ class SettingService
      */
     public function putUser(User $user, string $key, string $value): bool
     {
-        if ($user->isDefault()) {
+        if ($user->isGuest()) {
             session()->put($key, $value);
 
             return true;