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>

package.json

@@ -3,6 +3,7 @@
   "private": true,
   "packageManager": "pnpm@10.7.1",
   "engines": { "node": ">=22.12" },
+  "//": "pnpm 10 默认拦截依赖 install 脚本；onlyBuiltDependencies 白名单放行 esbuild（vite 需下载平台二进制）。Playwright 浏览器另行执行 `pnpm exec playwright install chromium`。",
   "scripts": {
     "lint": "turbo run lint",
     "typecheck": "turbo run typecheck",
@@ -16,12 +17,17 @@
     "e2e": "turbo run test:e2e"
   },
   "devDependencies": {
+    "@playwright/test": "^1.48.0",
     "turbo": "^2.3.0",
     "typescript": "^5.6.0",
     "prettier": "^3.3.0",
     "dotenv-cli": "^7.4.0",
     "eslint": "^9.0.0",
+    "eslint-plugin-vue": "^9.28.0",
     "typescript-eslint": "^8.0.0",
     "globals": "^16.0.0"
+  },
+  "pnpm": {
+    "onlyBuiltDependencies": ["esbuild"]
   }
 }