feat(ui): 无生信启动时隐藏扩展按钮

- 扩展按钮与生信跳转按钮互补显隐:生信可用时显示扩展、
  不可用时隐藏扩展并显示生信跳转(PlantAI-dev 9017 入口)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/components/layout/TopBar.vue

@@ -212,7 +212,7 @@ const iconRailBio = '<svg viewBox="0 0 24 24" fill="none" stroke="currentColor"
 
     <!-- 右上角快捷按钮(2026-09-15 自侧栏迁移;仅 desktop/laptop;图标+文字同行右对齐) -->
     <template v-if="tier === 'desktop' || tier === 'laptop'">
-      <button class="icon-btn top-rail-btn" type="button" :title="BF.extRailTitle" :aria-label="BF.extRailTitle"
+      <button v-if="bioflowOnline" class="icon-btn top-rail-btn" type="button" :title="BF.extRailTitle" :aria-label="BF.extRailTitle"
               @click="$emit('goto-extensions')">
         <span v-html="iconRailExt"></span>
         <span class="rail-label">{{ BF.extRailTitle }}</span>