💄 style(dashboard): 调整大屏仪表盘用户操作日志文字颜色

- 将用户名称颜色从白色改为深灰色(text-gray-800)
- 将操作描述颜色从半透明白色改为中灰色(text-gray-600)
- 将时间颜色从60%透明白色改为浅灰色(text-gray-500)

src/client/admin/pages/BigScreenDashboard.tsx

@@ -379,9 +379,9 @@ const BigScreenDashboard: React.FC = () => {
                   {item.icon}
                 </div>
                 <div className="flex-1">
-                  <div className="font-semibold text-white text-sm">{item.user}</div>
-                  <div className="text-white opacity-80 text-sm">{item.action}</div>
-                  <div className="text-white opacity-60 text-xs">{item.time}</div>
+                  <div className="font-semibold text-gray-800 text-sm">{item.user}</div>
+                  <div className="text-gray-600 text-sm">{item.action}</div>
+                  <div className="text-gray-500 text-xs">{item.time}</div>
                 </div>
               </div>
             ))}