chore(app): lint cleanups (const constructors, local function)

lib/components/sidebar_contents/gdpr_button.dart

@@ -76,8 +76,8 @@ class GdprButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return IconButton(
-      icon: const Icon(Icons.admin_panel_settings_outlined,
+    return const IconButton(
+      icon: Icon(Icons.admin_panel_settings_outlined,
           color: AppColors.textWhite, size: 28),
       onPressed: showConsentForm,
       tooltip: 'Ad consent & privacy choices',