refactor(mining-app): rename VIP等级 to 团队上级 and 直推人数 to 引荐人数

- Changed "VIP等级" label to "团队上级" in profile stats row
- Changed display value from vipLevel (V3 format) to unlockedBonusTiers (raw number)
- Changed "直推人数" label to "引荐人数" for consistency

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

frontend/mining-app/lib/presentation/pages/profile/profile_page.dart

@@ -252,7 +252,7 @@ class ProfilePage extends ConsumerWidget {
           ),
           _buildDivider(),
           _buildStatItem(
-            '直推人数',
+            '引荐人数',
             stats?.directReferralAdoptedCount.toString() ?? '0',
             isLoading,
           ),
@@ -264,8 +264,8 @@ class ProfilePage extends ConsumerWidget {
           ),
           _buildDivider(),
           _buildStatItem(
-            'VIP等级',
-            stats?.vipLevel ?? '-',
+            '团队上级',
+            stats?.unlockedBonusTiers.toString() ?? '0',
             isLoading,
           ),
         ],