1.追加：投票结束查看倒计时时间

2.修改：倒计时样式
3.优化：抽奖和投票倒计时代码统一

frontend_nuxt/composables/useCountdown.ts

@@ -0,0 +1,51 @@
+import { ref, onMounted, onBeforeUnmount } from 'vue'
+
+/**
+ * 通用倒计时 composable
+ * @param endTime 截止时间字符串或 Date 对象
+ * @returns { countdown, isEnded }
+ */
+export function useCountdown(endTime?: string | Date) {
+  const countdown = ref('')
+  const isEnded = ref(false)
+  let timer: ReturnType<typeof setInterval> | null = null
+
+  const update = () => {
+    if (!endTime) {
+      countdown.value = ''
+      isEnded.value = true
+      return
+    }
+    const diff = new Date(endTime).getTime() - Date.now()
+    if (diff <= 0) {
+      countdown.value = '已结束'
+      isEnded.value = true
+      if (timer) clearInterval(timer)
+      return
+    }
+    // 计算天、时、分、秒
+    const days = Math.floor(diff / (24 * 3600 * 1000))
+    const hours = Math.floor((diff % (24 * 3600 * 1000)) / 3600000)
+    const minutes = Math.floor((diff % 3600000) / 60000)
+    const seconds = Math.floor((diff % 60000) / 1000)
+
+    if (days > 0) {
+      countdown.value = `${days}天 ${hours}小时 ${minutes}分 ${seconds}秒`
+    } else if (hours > 0) {
+      countdown.value = `${hours}小时 ${minutes}分 ${seconds}秒`
+    } else {
+      countdown.value = `${minutes}分 ${seconds}秒`
+    }
+  }
+
+  onMounted(() => {
+    update()
+    timer = setInterval(update, 1000)
+  })
+
+  onBeforeUnmount(() => {
+    if (timer) clearInterval(timer)
+  })
+
+  return { countdown, isEnded }
+}