fix: refine mobile navigation and settings

frontend/src/App.vue

@@ -1254,7 +1254,7 @@ onUnmounted(() => {
     </aside>
 
     <div v-if="mobileMore" class="more-mask app-sheet-mask" @click.self="mobileMore=false;switchView('settings')"><section id="mobile-more-menu" class="more-sheet app-sheet app-sheet--actions" role="dialog" aria-modal="true" aria-label="更多导航" @click.stop><div class="more-sheet-head app-sheet__header"><b>更多</b><button class="icon" aria-label="关闭更多菜单" @click="mobileMore=false"><X/></button></div><div class="app-sheet__body"><button @click="switchView('settings')"><Settings/>设置与数据</button></div></section></div>
-    <nav class="bottom" aria-label="主要导航"><button :class="{active:activeView==='today'}" @click="switchView('today')"><ListTodo/><span>今天</span></button><button :class="{active:activeView==='habits'}" @click="switchView('habits')"><Repeat2/><span>习惯</span></button><button :class="{active:activeView==='countdowns'}" @click="switchView('countdowns')"><CalendarHeart/><span>倒数日</span></button><button :class="{active:activeView==='tasks'||activeView==='upcoming'||activeView==='trash'||activeView==='settings'}" @click="switchView('settings')"><Settings/><span>设置</span></button></nav>
+    <nav class="bottom" aria-label="主要导航"><button :class="{active:activeView==='today'}" :aria-current="activeView==='today' ? 'page' : undefined" @click="switchView('today')"><ListTodo/><span>今天</span></button><button :class="{active:activeView==='habits'}" :aria-current="activeView==='habits' ? 'page' : undefined" @click="switchView('habits')"><Repeat2/><span>习惯</span></button><button :class="{active:activeView==='countdowns'}" :aria-current="activeView==='countdowns' ? 'page' : undefined" @click="switchView('countdowns')"><CalendarHeart/><span>倒数日</span></button><button :class="{active:activeView==='settings'}" :aria-current="activeView==='settings' ? 'page' : undefined" @click="switchView('settings')"><Settings/><span>设置</span></button></nav>
     <FloatingAddButton v-if="['tasks','today','upcoming','habits','countdowns'].includes(activeView)" :label="activeView==='habits' ? '添加习惯' : activeView==='countdowns' ? '添加倒数日' : '添加任务'" @activate="activateFloatingAdd" />
     <Transition name="task-compose">
       <div v-if="taskComposeOpen" class="task-compose-mask app-sheet-mask" @click.self="closeTaskCompose">