feat: add GenerateMenuButton dropdown component

Implements a dropdown menu button component with generate and batch generate options. Includes click-outside and Escape-key menu closing behavior.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/GenerateMenuButton.vue

@@ -0,0 +1,68 @@
+<script setup lang="ts">
+import { onMounted, onUnmounted, ref } from 'vue'
+
+const emit = defineEmits<{
+  generate: []
+  batchGenerate: []
+}>()
+
+const open = ref(false)
+const rootRef = ref<HTMLElement | null>(null)
+
+function toggle(): void {
+  open.value = !open.value
+}
+
+function close(): void {
+  open.value = false
+}
+
+function select(action: 'generate' | 'batchGenerate'): void {
+  emit(action)
+  close()
+}
+
+function handleDocumentClick(event: MouseEvent): void {
+  if (!rootRef.value) return
+  if (!rootRef.value.contains(event.target as Node)) {
+    close()
+  }
+}
+
+function handleKeydown(event: KeyboardEvent): void {
+  if (event.key === 'Escape') {
+    close()
+  }
+}
+
+onMounted(() => {
+  document.addEventListener('click', handleDocumentClick)
+})
+
+onUnmounted(() => {
+  document.removeEventListener('click', handleDocumentClick)
+})
+</script>
+
+<template>
+  <div ref="rootRef" class="generate-menu" @keydown="handleKeydown">
+    <button
+      type="button"
+      data-testid="generate-menu-toggle"
+      :aria-expanded="open"
+      @click.stop="toggle"
+    >
+      生成教案 ▾
+    </button>
+    <ul v-if="open" class="generate-menu-list" role="menu">
+      <li role="menuitem">
+        <button type="button" data-testid="generate" @click="select('generate')">生成一篇</button>
+      </li>
+      <li role="menuitem">
+        <button type="button" data-testid="batch-generate" @click="select('batchGenerate')">
+          批量生成
+        </button>
+      </li>
+    </ul>
+  </div>
+</template>