perf: 优化体积，highlight.js按需导入与i18n按需加载 (#696)

* perf: 优化打包体积，highlight.js按需导入与i18n按需加载

1. highlight.js: 从全量导入改为 core + 注册27种常用语言，减少约500~800KB
2. i18n: 只同步加载en语言包，其他8种语言改为异步加载，首屏减少约350~400KB
3. 使用vue-i18n的setLocaleMessage API动态注册语言包
4. 新增switchLocale函数统一处理语言切换
5. 同步更新相关测试文件的mock路径和API适配

* 修复类型断言

tests/client/highlight-helper.test.ts

@@ -5,9 +5,10 @@ const highlightJsMock = vi.hoisted(() => ({
   highlight: vi.fn((content: string, { language }: { language: string }) => ({
     value: `<span class="mock-${language}">${content}</span>`,
   })),
+  registerLanguage: vi.fn(),
 }))
 
-vi.mock('highlight.js', () => ({
+vi.mock('highlight.js/lib/core', () => ({
   default: highlightJsMock,
 }))
 

tests/client/i18n-coverage.test.ts

@@ -1,12 +1,16 @@
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, beforeAll } from 'vitest'
 import { readdirSync, readFileSync } from 'fs'
 import { join, relative } from 'path'
 
 import { changelog } from '@/data/changelog'
-import { messages, rawMessages } from '@/i18n/messages'
+import { loadLocale, supportedLocales } from '@/i18n/messages'
+import en from '@/i18n/locales/en'
+import { createI18n } from 'vue-i18n'
 
 const SOURCE_ROOT = join(process.cwd(), 'packages/client/src')
 
+const allMessages: Record<string, Record<string, unknown>> = { en }
+
 function walkFiles(dir: string, files: string[] = []): string[] {
   for (const entry of readdirSync(dir, { withFileTypes: true })) {
     const path = join(dir, entry.name)
@@ -93,15 +97,23 @@ function labelLength(value: unknown): number {
 }
 
 describe('i18n locale coverage', () => {
-  // Keys that are newly added but not yet translated in all locales
   const ALLOWED_MISSING_KEYS = new Set([
     'changelog.new_0_5_4_7',
     'chat.sessionNotFound',
   ])
 
+  beforeAll(async () => {
+    const results = await Promise.all(
+      supportedLocales.filter(l => l !== 'en').map(async l => {
+        const msgs = await loadLocale(l)
+        if (msgs) allMessages[l] = msgs
+      }),
+    )
+  })
+
   it('defines every statically referenced translation key in the English source locale', () => {
     const missing = collectLiteralTranslationKeys()
-      .filter((key) => !hasPath(rawMessages.en, key))
+      .filter((key) => !hasPath(en, key))
       .filter((key) => !ALLOWED_MISSING_KEYS.has(key))
 
     expect(missing).toEqual([])
@@ -109,7 +121,7 @@ describe('i18n locale coverage', () => {
 
   it('defines every statically referenced translation key in effective runtime messages', () => {
     const requiredKeys = collectLiteralTranslationKeys()
-    const missing = Object.entries(messages).flatMap(([locale, localeMessages]) =>
+    const missing = Object.entries(allMessages).flatMap(([locale, localeMessages]) =>
       requiredKeys
         .filter((key) => !hasPath(localeMessages, key))
         .filter((key) => !ALLOWED_MISSING_KEYS.has(key))

tests/client/sidebar-search.test.ts

@@ -42,6 +42,9 @@ vi.mock('vue-i18n', () => ({
   useI18n: () => ({
     t: (key: string) => key,
   }),
+  createI18n: () => ({
+    global: { locale: { value: 'en' }, setLocaleMessage: vi.fn() },
+  }),
 }))
 
 vi.mock('@/composables/useTheme', () => ({