docs(input-menu/select-menu): add countries picker examples

docs/app/components/content/examples/select-menu/SelectMenuCountriesExample.vue

@@ -0,0 +1,40 @@
+<script setup lang="ts">
+const { data: countries, status, execute } = await useLazyFetch<{
+  name: string
+  code: string
+  emoji: string
+}[]>('/api/countries.json', {
+  immediate: false
+})
+
+function onOpen() {
+  if (!countries.value?.length) {
+    execute()
+  }
+}
+</script>
+
+<template>
+  <USelectMenu
+    :items="countries || []"
+    :loading="status === 'pending'"
+    label-key="name"
+    :filter="['name']"
+    :search-input="{ icon: 'i-lucide-search' }"
+    placeholder="Select country"
+    class="w-48"
+    @update:open="onOpen"
+  >
+    <template #leading="{ modelValue, ui }">
+      <span v-if="modelValue" class="size-5 text-center">
+        {{ modelValue?.emoji }}
+      </span>
+      <UIcon v-else name="i-lucide-earth" :class="ui.leadingIcon()" />
+    </template>
+    <template #item-leading="{ item }">
+      <span class="size-5 text-center">
+        {{ item.emoji }}
+      </span>
+    </template>
+  </USelectMenu>
+</template>