Refactor helper drift in lib: centralize theme/translation and remove app() hotspots

lib/Service/User/UserSettingsGateway.php

@@ -35,6 +35,24 @@ class UserSettingsGateway
         return $this->settingsAppGateway->getAppTheme();
     }
 
+    /**
+     * @return array<string, string>
+     */
+    public function appThemes(): array
+    {
+        return $this->settingsAppGateway->listThemes();
+    }
+
+    public function defaultTheme(): string
+    {
+        return $this->settingsAppGateway->resolveDefaultTheme();
+    }
+
+    public function normalizeTheme(?string $theme): string
+    {
+        return $this->settingsAppGateway->normalizeTheme($theme);
+    }
+
     public function getUserInactivityDeactivateDays(): int
     {
         return $this->settingsUserLifecycleGateway->getUserInactivityDeactivateDays();