fix(game): 修复底部塔面板不可见问题，改用React层实现，并用AI素材替换Graphics像素块

app/page.tsx

@@ -15,8 +15,16 @@ export default function GameCover() {
   return (
     <main
       className="crt-overlay relative w-full min-h-screen flex flex-col items-center justify-center overflow-hidden"
-      style={{ backgroundColor: '#0F0F23' }}
+      style={{
+        backgroundColor: '#0F0F23',
+        backgroundImage: 'url(/game-assets/cover-bg.png)',
+        backgroundSize: 'cover',
+        backgroundPosition: 'center',
+      }}
     >
+      {/* 深色叠加层，确保文字可读 */}
+      <div className="absolute inset-0" style={{ backgroundColor: 'rgba(10,10,30,0.72)' }} />
+
       {/* CRT 流动扫描线 */}
       <div className="game-cover-scanline" />