fix(mining-app): 已解锁上层数 = unlockedBonusTiers × 5

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/mining-app/lib/presentation/pages/contribution/contribution_page.dart

@@ -588,7 +588,7 @@ class ContributionPage extends ConsumerWidget {
               _buildTeamStatItem(
                 context,
                 '已解锁上',
-                contribution?.unlockedBonusTiers.toString(),
+                contribution != null ? (contribution.unlockedBonusTiers * 5).toString() : null,
                 '',
                 isLoading,
               ),