feat(perf,ux): implement performance and UX optimizations

Phase 2: Performance Optimizations
- Implement dynamic imports for non-critical sections
- Add loading skeletons for lazy-loaded components
- Optimize bundle size with code splitting
- Enable SSR for dynamic components

Phase 3: UX Optimizations
- Create ErrorBoundary component for graceful error handling
- Add Toast notification component for user feedback
- Implement success/error notifications in contact form
- Add error handling with user-friendly messages

Files modified:
- src/app/(marketing)/page.tsx: Dynamic imports for sections
- src/app/(marketing)/layout.tsx: Error boundary integration
- src/components/sections/contact-section.tsx: Toast notifications
- src/components/ui/error-boundary.tsx: New error boundary component
- src/components/ui/toast.tsx: New toast notification component

Impact:
- Reduced initial bundle size
- Faster page load times
- Better error handling
- Improved user feedback
- Enhanced user experience

src/components/ui/toast.tsx

@@ -0,0 +1,64 @@
+'use client';
+
+import { useEffect, useState } from 'react';
+import { CheckCircle2, X, AlertCircle, Info } from 'lucide-react';
+
+interface ToastProps {
+  message: string;
+  type?: 'success' | 'error' | 'info';
+  duration?: number;
+  onClose: () => void;
+}
+
+export function Toast({ 
+  message, 
+  type = 'success', 
+  duration = 3000, 
+  onClose 
+}: ToastProps) {
+  const [isVisible, setIsVisible] = useState(true);
+
+  useEffect(() => {
+    const timer = setTimeout(() => {
+      setIsVisible(false);
+      setTimeout(onClose, 300);
+    }, duration);
+
+    return () => clearTimeout(timer);
+  }, [duration, onClose]);
+
+  const icons = {
+    success: <CheckCircle2 className="h-5 w-5 text-green-500" />,
+    error: <AlertCircle className="h-5 w-5 text-red-500" />,
+    info: <Info className="h-5 w-5 text-blue-500" />
+  };
+
+  const bgColors = {
+    success: 'bg-green-50 border-green-200',
+    error: 'bg-red-50 border-red-200',
+    info: 'bg-blue-50 border-blue-200'
+  };
+
+  return (
+    <div
+      className={`fixed bottom-4 right-4 z-50 flex items-center gap-3 px-4 py-3 bg-white rounded-lg shadow-lg border transition-all duration-300 ${
+        isVisible ? 'opacity-100 translate-y-0' : 'opacity-0 translate-y-2'
+      } ${bgColors[type]}`}
+      role="alert"
+      aria-live="polite"
+    >
+      {icons[type]}
+      <p className="text-sm font-medium text-[#1C1C1C]">{message}</p>
+      <button
+        onClick={() => {
+          setIsVisible(false);
+          setTimeout(onClose, 300);
+        }}
+        className="ml-2 text-gray-400 hover:text-gray-600 transition-colors"
+        aria-label="关闭提示"
+      >
+        <X className="h-4 w-4" />
+      </button>
+    </div>
+  );
+}