feat(viewer): vite vue3 scaffold with routing and i18n

- apps/viewer (@photo/viewer): Vite 5 + Vue 3.4 + TS 最小骨架（无 Pinia/UI 库）
- router: /a/:token 活动页 + /a/:token/p/:photoId 单图深链（复用活动页组件）
- i18n: vue-i18n 9，zh-CN/en 词条，localStorage(viewer.locale) 持久 +
  navigator.language 检测兜底 zh-CN；顶栏语言切换组件；文案全量走 i18n
- api client: 类型化 fetch 封装（契约生成类型直连），错误信封 → ApiError，
  错误码 → i18n key 映射表（src/api/errors.ts）
- scripts: dev/build/preview/test(vitest 10 例)/test:e2e(Playwright 冒烟,
  webServer 自拉 dev)/lint/vue-tsc 全部接入 turbo
- root: +@playwright/test、+eslint-plugin-vue（flat config 收敛到 apps/**/*.vue）、
  pnpm.onlyBuiltDependencies 放行 esbuild

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

apps/viewer/src/i18n/locales/en.ts

@@ -0,0 +1,20 @@
+export default {
+  app: { title: 'Live Gallery' },
+  home: { hint: 'Open an album link to start viewing' },
+  album: { emptyNotice: 'Photos coming soon' },
+  lang: { switch: 'Switch language' },
+  route: { tokenLabel: 'Album token', photoLabel: 'Photo' },
+  errors: {
+    albumNotFound: 'Album not found',
+    albumNotAvailable: 'Album unavailable',
+    photoNotFound: 'Photo not found',
+    notFound: 'Page not found',
+    authExpired: 'Session expired',
+    forbidden: 'Access denied',
+    rateLimited: 'Too many requests, please try again later',
+    validationFailed: 'Invalid request',
+    internal: 'Service temporarily unavailable, please try again later',
+    unknown: 'Something went wrong, please try again later',
+    network: 'Network error, please check your connection',
+  },
+};