feat: 完成navbar隐藏优化和侧边栏冻结功能

- 优化navbar滚动隐藏逻辑，更敏感响应
- 添加返回顶部按钮，固定在右下角
- 实现profile页面侧边栏真正冻结效果
- 修复首页滑动指示器位置
- 优化整体布局确保首屏内容完整显示

src/components/ScrollToTop.tsx

@@ -0,0 +1,65 @@
+'use client';
+
+import { useState, useEffect } from 'react';
+import { motion, AnimatePresence } from 'framer-motion';
+
+export default function ScrollToTop() {
+  const [showScrollTop, setShowScrollTop] = useState(false);
+
+  useEffect(() => {
+    let ticking = false;
+    
+    const handleScroll = () => {
+      if (!ticking) {
+        window.requestAnimationFrame(() => {
+          const currentScrollY = window.scrollY;
+          // 显示返回顶部按钮（滚动超过300px）
+          setShowScrollTop(currentScrollY > 300);
+          ticking = false;
+        });
+        ticking = true;
+      }
+    };
+
+    window.addEventListener('scroll', handleScroll, { passive: true });
+    return () => window.removeEventListener('scroll', handleScroll);
+  }, []);
+
+  const scrollToTop = () => {
+    window.scrollTo({
+      top: 0,
+      behavior: 'smooth'
+    });
+  };
+
+  return (
+    <AnimatePresence>
+      {showScrollTop && (
+        <motion.button
+          initial={{ opacity: 0, scale: 0.8, y: 20 }}
+          animate={{ opacity: 1, scale: 1, y: 0 }}
+          exit={{ opacity: 0, scale: 0.8, y: 20 }}
+          transition={{ duration: 0.2, ease: 'easeOut' }}
+          onClick={scrollToTop}
+          className="fixed bottom-6 right-6 w-12 h-12 bg-gradient-to-br from-orange-500 to-orange-600 hover:from-orange-600 hover:to-orange-700 text-white rounded-full shadow-lg hover:shadow-xl transition-all duration-200 flex items-center justify-center z-[100] group"
+          whileHover={{ scale: 1.1, y: -2 }}
+          whileTap={{ scale: 0.9 }}
+        >
+          <svg 
+            className="w-5 h-5 transition-transform duration-200 group-hover:-translate-y-0.5" 
+            fill="none" 
+            stroke="currentColor" 
+            viewBox="0 0 24 24"
+          >
+            <path 
+              strokeLinecap="round" 
+              strokeLinejoin="round" 
+              strokeWidth={2} 
+              d="M5 10l7-7m0 0l7 7m-7-7v18" 
+            />
+          </svg>
+        </motion.button>
+      )}
+    </AnimatePresence>
+  );
+}