feat: 添加全屏水印（羚牛氢能-时间戳）

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/App.tsx

@@ -393,8 +393,17 @@ export default function App() {
 
   const SUMMARY = summary!;
 
+  const watermarkText = `羚牛氢能-${new Date().toLocaleString('zh-CN', { year: 'numeric', month: '2-digit', day: '2-digit', hour: '2-digit', minute: '2-digit', second: '2-digit', hour12: false }).replace(/\//g, '-')}`;
+
   return (
-    <div className="min-h-screen bg-[#F8F9FB] text-gray-800 font-sans p-6 pb-20 md:pb-6">
+    <div className="min-h-screen bg-[#F8F9FB] text-gray-800 font-sans p-6 pb-20 md:pb-6 relative">
+      {/* Watermark */}
+      <div className="fixed inset-0 pointer-events-none z-[9999] overflow-hidden" style={{ opacity: 0.06 }}>
+        <div className="absolute inset-0" style={{
+          backgroundImage: `url("data:image/svg+xml,${encodeURIComponent(`<svg xmlns='http://www.w3.org/2000/svg' width='320' height='200'><text x='50%' y='50%' text-anchor='middle' dominant-baseline='middle' font-size='14' font-family='sans-serif' fill='%23000' transform='rotate(-25 160 100)'>${watermarkText}</text></svg>`)}")`,
+          backgroundRepeat: 'repeat',
+        }} />
+      </div>
       {/* Compact Header Bar */}
       <div className="sticky top-0 z-40 -mx-6 -mt-6 mb-4 bg-white/95 backdrop-blur-sm border-b border-gray-100/80">
         {/* Title row */}