fix: remove bing redirect, fix modal centering across all pages

- DemoDisclaimerModal: remove bing redirect on "稍后再说", just close
- App.tsx: remove will-change:transform from AnimatedRoute which created
  a new containing block and broke fixed positioning for all modals
- OnboardingGuide: add Portal as extra safety for centering

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

src/App.tsx

@@ -73,7 +73,6 @@ function AnimatedRoute({ children, pageName }: { children: React.ReactNode; page
       initial="initial"
       animate="animate"
       exit="exit"
-      style={{ willChange: 'transform, opacity' }}
     >
       <PageErrorBoundary pageName={pageName}>
         {children}

src/components/DemoDisclaimerModal.tsx

@@ -70,8 +70,6 @@ export function DemoDisclaimerModal() {
     setTimeout(() => {
       setIsOpen(false);
       setIsClosing(false);
-      // 跳转到必应
-      window.location.href = 'https://www.bing.com';
     }, 300);
   };
 

src/components/OnboardingGuide.tsx

@@ -1,4 +1,5 @@
 import React, { useState, useEffect } from 'react';
+import { createPortal } from 'react-dom';
 import { motion, AnimatePresence } from 'framer-motion';
 import { X, ChevronRight, ChevronLeft, CheckCircle, Factory, ClipboardList, Share2, Package } from 'lucide-react';
 import { useNavigate } from 'react-router-dom';
@@ -136,7 +137,7 @@ export function OnboardingGuide({ role, isOpen, onClose }: OnboardingGuideProps)
   // 如果已完成引导或不显示，返回null
   if (!isOpen || isCompleted) return null;
 
-  return (
+  return createPortal(
     <div className="fixed inset-0 bg-black/60 backdrop-blur-sm flex items-center justify-center z-50 p-4">
       <motion.div
         initial={{ opacity: 0, scale: 0.95, y: 20 }}
@@ -244,7 +245,8 @@ export function OnboardingGuide({ role, isOpen, onClose }: OnboardingGuideProps)
           </div>
         </div>
       </motion.div>
-    </div>
+    </div>,
+    document.body
   );
 }