fix(mobile): correct community benefit description

Changed from "有资格获得 3% 的社区福利" to "每新增认种 1 棵可获得 80 USDT"
which accurately reflects the actual community benefit rule.

🤖 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

@@ -1886,7 +1886,7 @@ class _ProfilePageState extends ConsumerState<ProfilePage> {
               Expanded(
                 child: Text(
                   _communityBenefitActive
-                      ? '有资格获得 3% 的社区福利'
+                      ? '每新增认种 1 棵可获得 80 USDT'
                       : '需团队认种达到 $_communityInitialTarget 棵激活',
                   style: TextStyle(
                     fontSize: 14,