feat: add floating new message container

frontend_nuxt/components/NewMessageContainer.vue

@@ -0,0 +1,33 @@
+<template>
+  <div class="new-message-container" :style="{ bottom: bottom + 'px' }" @click="$emit('click')">
+    {{ count }} 条新消息，点击查看
+  </div>
+</template>
+
+<script setup>
+const props = defineProps({
+  count: {
+    type: Number,
+    default: 0,
+  },
+  bottom: {
+    type: Number,
+    default: 0,
+  },
+})
+</script>
+
+<style scoped>
+.new-message-container {
+  position: absolute;
+  left: 50%;
+  transform: translateX(-50%);
+  background-color: var(--primary-color);
+  color: #fff;
+  padding: 6px 16px;
+  border-radius: 20px;
+  cursor: pointer;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
+  z-index: 50;
+}
+</style>