fix: refine Today mobile hierarchy

frontend/src/App.vue

@@ -1708,9 +1708,10 @@ onUnmounted(() => {
       <template v-else>
         <section v-if="activeView==='today'" class="today-context" aria-label="今日概览">
           <TodayEnvironmentStrip :environment="todayEnvironment" :loading="todayEnvironmentLoading" :failed="todayEnvironmentError" />
-          <h1 class="today-page-title">今天</h1>
-          <p class="today-remaining">还有 {{ todayTaskRemaining + todayHabitRemaining }} 项待完成</p>
-          <CompletedFilterPill v-model="showCompleted" class="today-inline-filter" />
+          <div class="today-heading">
+            <div><h1 class="today-page-title">今天</h1><p class="today-remaining">还有 {{ todayTaskRemaining + todayHabitRemaining }} 项待完成</p></div>
+            <CompletedFilterPill v-model="showCompleted" class="today-inline-filter" />
+          </div>
         </section>
         <section v-if="activeView==='tasks'" class="list-page-context">
           <div><h1 class="list-page-title" :title="activeName">{{ activeName }}</h1><p class="list-page-summary">{{ taskOpenTotal === null ? '待完成统计暂不可用' : `还有 ${taskOpenTotal} 项待完成` }}</p></div>
@@ -1755,6 +1756,7 @@ onUnmounted(() => {
         </div>
       </div>
       </template>
+      <button v-if="activeView==='today' && showFloatingAdd" class="today-inline-add" type="button" aria-label="添加任务" @click="openTaskCompose"><Plus/><span>添加任务</span></button>
     </main>
 
     <AppSheet v-if="selectedTask" :open="true" :modal="compactLayout" variant="detail" panel-class="detail" title-id="task-detail-title" :close-on-scrim="compactLayout" :busy="taskDetailBusy" @close="closeTaskDetail" @submit.prevent="saveSelectedTaskChanges">
@@ -1789,7 +1791,7 @@ onUnmounted(() => {
     </AppSheet>
 
     <nav class="bottom" :inert="memoBackgroundInert ? true : undefined" 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','memos'].includes(activeView)" :show="showFloatingAdd" :label="activeView==='habits' ? '添加习惯' : activeView==='countdowns' ? '添加倒数日' : activeView==='memos' ? '添加备忘录' : '添加任务'" @activate="activateFloatingAdd" />
+    <FloatingAddButton v-if="activeView!=='today' && ['tasks','upcoming','habits','countdowns','memos'].includes(activeView)" :show="showFloatingAdd" :label="activeView==='habits' ? '添加习惯' : activeView==='countdowns' ? '添加倒数日' : activeView==='memos' ? '添加备忘录' : '添加任务'" @activate="activateFloatingAdd" />
     <AppSheet :open="taskComposeOpen" variant="create" panel-class="task-compose-sheet" title-id="task-compose-title" initial-focus=".task-compose-input" :style="taskComposeStyle" @close="closeTaskCompose" @submit.prevent="submitTaskCompose">
           <header class="app-sheet__header"><div><h2 id="task-compose-title">{{ taskComposeTitle }}</h2></div><button class="icon" type="button" aria-label="关闭添加任务" @click="closeTaskCompose"><X/></button></header>
           <div class="app-sheet__body">