fix: 移除 Detail.jsx 外层 motion.div，修复路由切换白屏问题

frontend/src/pages/activity/Detail.jsx

@@ -351,13 +351,7 @@ const ActivityDetail = () => {
   };
 
   return (
-    <motion.div
+    <div style={{ background: '#1f1f1f', minHeight: '100vh', color: '#fff' }}>
-      initial="initial"
-      animate="animate"
-      exit="exit"
-      variants={pageTransition}
-      style={{ background: '#1f1f1f', minHeight: '100vh', color: '#fff' }}
-    >
       {/* Sticky Header */}
       <motion.div
         style={{
@@ -623,7 +617,7 @@ const ActivityDetail = () => {
          </div>
       </Modal>
 
-    </motion.div>
+    </div>
   );
 };