fix(PortalHeader): 激活2025年贡献者大会下拉选项

- 移除注释标记以启用2025年选项
- 保持下拉菜单结构和分隔符设置

src/components/PortalHeader.vue

@@ -106,7 +106,8 @@
                 >贡献者大会</span
               >
               <el-dropdown-menu slot="dropdown">
-                <el-dropdown-item command="three">2024</el-dropdown-item>
+                <el-dropdown-item command="four">2025</el-dropdown-item>
+                <el-dropdown-item command="three" divided>2024</el-dropdown-item>
                 <el-dropdown-item command="one" divided>2023</el-dropdown-item>
                 <el-dropdown-item command="two" divided>2022</el-dropdown-item>
               </el-dropdown-menu>