Phase 006: migrate the chat page from naive-ui to Arco Design Vue

Swaps the rendering layer only. Chat store logic, keyboard handling, and the
/chat-run Socket.IO contract are untouched, so a mixed UI cannot hide a chat
regression behind a library swap.

Arco's dropdowns take their items from a #content slot of a-doption children
rather than a droplist prop, and Arco Triggers cannot be nested, so the two
toolbar menus lost their a-tooltip in favour of a native title. Both rules are
recorded in docs/arco-mapping.md, and tests/e2e/chat-input-dropdown.spec.ts plus
tests/e2e/chat-rendering-smoke.spec.ts keep the menus, the streaming markdown
rendering, and the no-Arco-inside-the-bubble red line from regressing silently.

tests/client/voice-dialogue-controls.test.ts

@@ -3,6 +3,7 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { flushPromises, mount } from '@vue/test-utils'
 import { createTestingPinia } from '@pinia/testing'
 import { defineComponent } from 'vue'
+import ArcoVue from '@arco-design/web-vue'
 import { useChatStore } from '@/stores/hermes/chat'
 import VoiceDialogueControls from '@/components/hermes/chat/VoiceDialogueControls.vue'
 import ChatInput from '@/components/hermes/chat/ChatInput.vue'
@@ -73,16 +74,23 @@ vi.mock('vue-i18n', () => ({
   }),
 }))
 
-vi.mock('naive-ui', () => ({
-  NButton: { template: '<button type="button" v-bind="$attrs"><slot /><slot name="icon" /></button>' },
-  NTooltip: { template: '<div><slot name="trigger" /><slot /></div>' },
-  NSwitch: { template: '<button type="button"></button>' },
-  NDropdown: { template: '<div><slot /></div>' },
-  NModal: { template: '<div><slot /><slot name="footer" /></div>' },
-  NInputNumber: { template: '<input />' },
-  NPopselect: { template: '<div><slot /></div>' },
-  useMessage: () => ({ error: vi.fn(), success: vi.fn() }),
-}))
+// Arco's imperative message API needs a live DOM; the rest renders for real.
+vi.mock('@arco-design/web-vue', async () => {
+  const actual =
+    await vi.importActual<typeof import('@arco-design/web-vue')>(
+      '@arco-design/web-vue',
+    )
+  return {
+    ...actual,
+    Message: {
+      success: vi.fn(),
+      error: vi.fn(),
+      warning: vi.fn(),
+      info: vi.fn(),
+      loading: vi.fn(),
+    },
+  }
+})
 
 vi.mock('@/api/hermes/sessions', () => ({
   fetchContextLength: vi.fn().mockResolvedValue(256000),
@@ -174,7 +182,7 @@ describe('VoiceDialogueControls', () => {
     const wrapper = mount(ChatInput, {
       ...options,
       global: {
-        plugins: [pinia],
+        plugins: [pinia, ArcoVue],
         ...options.global,
       },
     })