style: 语言切换改纯文字 + 移到登录注册左边

- 去掉边框、背景、圆角，纯文字 CN/EN
- 去掉 SVG 地球图标
- 从右侧移到登录注册按钮左边

public/header.html

@@ -27,6 +27,12 @@
       </div>
     </div>
     <div class="nav-right">
+      <!-- 语言切换（始终显示，放在最左边） -->
+      <div class="lang-switch nav-desktop-link" id="langSwitch" onclick="i18n.toggle()">
+        <span class="lang-text">CN</span>
+        <span class="lang-sep">/</span>
+        <span class="lang-alt">EN</span>
+      </div>
       <!-- 未登录状态 -->
       <div class="no-login nav-desktop-link d-none">
         <span class="nav-text-link" id="loginBtn" data-i18n="nav_login">登录</span>
@@ -52,13 +58,6 @@
           <div class="login-menu-item" id="logout" data-i18n="menu_logout">退出账户</div>
         </div>
       </div>
-      <!-- 语言切换（始终显示） -->
-      <div class="lang-switch nav-desktop-link" id="langSwitch" onclick="i18n.toggle()">
-        <svg class="lang-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round"><circle cx="12" cy="12" r="10"/><path d="M2 12h20"/><path d="M12 2a15.3 15.3 0 0 1 4 10 15.3 15.3 0 0 1-4 10 15.3 15.3 0 0 1-4-10 15.3 15.3 0 0 1 4-10z"/></svg>
-        <span class="lang-text">CN</span>
-        <span class="lang-sep">/</span>
-        <span class="lang-alt">EN</span>
-      </div>
       <!-- 移动端汉堡菜单按钮 -->
       <button class="mobile-menu-toggle" id="mobileMenuToggle" aria-label="Toggle navigation">
         <img src="/web/BlackFruit-web/assets/img/header/bar.svg" alt="Menu" class="mobile-menu-icon">