fix: remove extra styling from StatisticsPlaceholder

Remove unspecified styling properties to match spec exactly.

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

src/pages/components/StatisticsPlaceholder.tsx

@@ -13,13 +13,7 @@ const StatisticsPlaceholder: React.FC = () => {
       }}
     >
       {/* 未来扩展：统计数据卡片、图表、报表等 */}
-      <div
+      <div>
-        style={{
-          color: '#bfbfbf',
-          fontSize: '16px',
-          textAlign: 'center',
-        }}
-      >
         {/* 当前阶段：完全空白，便于未来扩展 */}
       </div>
     </div>