feat(chat): add right-click context menus on messages (M8.9)

Reusable ContextMenu.vue glass-card component positioned at cursor.
Messages get Copy, Reply, Edit (user), Regenerate (assistant), and
Branch from here options. Closes on Escape or outside click.

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

packages/app/src/components/chat/ChatMessage.vue

@@ -3,6 +3,7 @@
     class="group/msg flex animate-fade-up-fast"
     :class="isUser ? 'justify-end' : 'justify-start'"
     :style="{ animationDelay: `${index * 30}ms` }"
+    @contextmenu.prevent="openContextMenu"
   >
     <div class="relative max-w-[85%] md:max-w-[75%]">
       <!-- Action buttons (hover on desktop, always visible on touch) -->
@@ -248,12 +249,23 @@
       </div>
       </div>
     </div>
+
+    <!-- Context menu -->
+    <ContextMenu ref="contextMenuRef">
+      <ContextMenuItem v-if="isUser" @click="startEditingFromMenu">Edit</ContextMenuItem>
+      <ContextMenuItem v-if="!isUser" @click="emitRegenerate">Regenerate</ContextMenuItem>
+      <ContextMenuItem @click="emitReply">Reply</ContextMenuItem>
+      <ContextMenuItem v-if="!isUser" @click="emitBranch">Branch from here</ContextMenuItem>
+      <ContextMenuItem @click="copyContent">Copy</ContextMenuItem>
+    </ContextMenu>
   </div>
 </template>
 
 <script setup lang="ts">
 import { computed, ref, nextTick } from 'vue'
 import MarkdownIt from 'markdown-it'
+import ContextMenu from '@/components/ui/ContextMenu.vue'
+import ContextMenuItem from '@/components/ui/ContextMenuItem.vue'
 import type { Message, WebSearchResult } from '@aiui/core/types/message'
 import type { Film, Song, Podcast, Book, TVSeries, ImageItem, Place } from '@aiui/core/types/content'
 import { useContentPanel, type MagazineSection } from '@/composables/useContentPanel'
@@ -497,4 +509,36 @@ function handleBubbleClick() {
   }
   if (hasContext.value) openPanel()
 }
+
+// Context menu
+const contextMenuRef = ref<InstanceType<typeof ContextMenu> | null>(null)
+
+function openContextMenu(e: MouseEvent) {
+  contextMenuRef.value?.open(e.clientX, e.clientY)
+}
+
+function startEditingFromMenu() {
+  contextMenuRef.value?.close()
+  startEditing()
+}
+
+function emitRegenerate() {
+  contextMenuRef.value?.close()
+  emit('regenerate')
+}
+
+function emitReply() {
+  contextMenuRef.value?.close()
+  emit('reply', props.message.id, props.message.content)
+}
+
+function emitBranch() {
+  contextMenuRef.value?.close()
+  emit('branch', props.message.id)
+}
+
+function copyContent() {
+  contextMenuRef.value?.close()
+  navigator.clipboard.writeText(props.message.content).catch(() => {})
+}
 </script>