refactor(ui): 引荐人数改为引荐

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

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

@@ -559,7 +559,7 @@ class ContributionPage extends ConsumerWidget {
             children: [
               _buildTeamStatItem(
                 context,
-                '引荐人数',
+                '引荐',
                 contribution?.directReferralAdoptedCount.toString(),
                 '',
                 isLoading,