fix(练习): 修正底部固定区域偏移方式

将 mb-8 改为 pb-8，使 sticky bottom-0 元素真正向上偏移

via [HAPI](https://hapi.run)

Co-Authored-By: HAPI <noreply@hapi.run>

src/pages/ProcessPracticePage.tsx

@@ -423,7 +423,7 @@ export default function ProcessPracticePage() {
       </div>
 
       {/* 底部固定区域（粘附底部，参与文档流） */}
-      <div className="sticky bottom-0 bg-white/60 dark:bg-gray-800/60 backdrop-blur-md border-t border-gray-200 dark:border-gray-700 z-10 mb-8">
+      <div className="sticky bottom-0 bg-white/60 dark:bg-gray-800/60 backdrop-blur-md border-t border-gray-200 dark:border-gray-700 z-10 pb-8">
         <div className="max-w-7xl mx-auto px-6">
           {/* 输入区域 */}
           <div className="py-3 border-b border-gray-200/50 dark:border-gray-700/50">