refactor: Simplify platform-specific icon handling in AppCustomizationPage and ProfilePage

- Replaced direct platform checks with a utility method `UiUtils.platformIcon` for better readability and maintainability.
- Updated localization strings for app customization to enhance clarity and consistency across multiple languages.
- Adjusted icon colors in the UI to ensure proper theming and visual consistency.

lib/l10n/app_nl.arb

@@ -233,8 +233,8 @@
   "deleteFolderTitle": "Map verwijderen",
   "deleteFolderMessage": "Deze map en zijn toewijzingen worden verwijderd.",
   "failedToDeleteFolder": "Kan map niet verwijderen",
-  "aboutApp": "Over de app",
-  "aboutAppSubtitle": "Conduit-informatie en links",
+  "aboutApp": "Over",
+  "aboutAppSubtitle": "Conduit informatie en links",
   "web": "Web",
   "imageGen": "Afbeeldingsgeneratie",
   "pinned": "Vastgepind",
@@ -303,8 +303,8 @@
     "description": "Toont hoe lang de assistent dacht voordat hij antwoordde.",
     "placeholders": {"duration": {"type": "String", "example": "3s"}}
   },
-  "appCustomization": "App-aanpassing",
-  "appCustomizationSubtitle": "Personaliseer hoe namen en UI worden weergegeven",
+  "appCustomization": "Aanpassing",
+  "appCustomizationSubtitle": "Thema, taal, stem en quickpills",
   "quickActionsDescription": "Kies maximaal twee snelkoppelingen om vast te pinnen bij de composer",
   "chatSettings": "Chat",
   "sendOnEnter": "Verzenden met Enter",