fix(mobile): reduce direct referral list item spacing

- Row gap: 8px → 4px
- Vertical padding: 12px → 8px

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/profile/presentation/pages/profile_page.dart

@@ -1515,9 +1515,9 @@ class _ProfilePageState extends ConsumerState<ProfilePage> {
         ),
         const SizedBox(height: 8),
         ..._referrals.map((referral) => Padding(
-          padding: const EdgeInsets.only(bottom: 8),
+          padding: const EdgeInsets.only(bottom: 4),
           child: Container(
-            padding: const EdgeInsets.all(12),
+            padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
             decoration: BoxDecoration(
               color: const Color(0xCCFFF5E6),
               borderRadius: BorderRadius.circular(8),