新分支：Vite+React19+TS+Tailwind v4 重新搭建，先跑通四级响应式布局壳

不再沿用旧 im_webapp 的技术栈（webpack + class组件 + 15000行全局CSS + 手搓History路由），
按业务重新选型：Vite/React Router/Zustand预留/TanStack Query/保留tinode-sdk真实依赖
（协议客户端本身没有重写的业务理由）。新代码放在 web/ 子目录，旧代码原样保留在仓库根目录，
两者共存到重写完成。

这一步先验证布局壳本身：NavRail（消息/通讯录/收藏/文件助手/通话记录/设置）+ 会话列表 +
主区域 + 详情栏，按设计稿的四档断点（<640/640-959/960-1279/≥1280）用真实浏览器宽度逐档验证
过——两列及以下"列表/主区域二选一+返回键"、三列"详情栏抽屉化"、四列"详情栏常驻"均已用
真实点击/返回验证正确，不是只看了截图。会话列表和聊天内容目前是占位数据，业务数据接入和
Tinode连接是下一步。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/package.json

@@ -0,0 +1,32 @@
+{
+  "name": "web",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc -b && vite build",
+    "lint": "oxlint",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "react": "^19.2.8",
+    "react-dom": "^19.2.8",
+    "react-router-dom": "^7.9.6",
+    "zustand": "^5.0.9",
+    "@tanstack/react-query": "^5.90.5",
+    "tinode-sdk": "^0.25.3",
+    "react-intl": "^7.1.6"
+  },
+  "devDependencies": {
+    "@types/node": "^24.13.3",
+    "@types/react": "^19.2.18",
+    "@types/react-dom": "^19.2.4",
+    "@vitejs/plugin-react": "^6.1.0",
+    "oxlint": "^1.79.0",
+    "typescript": "^5.6.0",
+    "vite": "^8.2.2",
+    "tailwindcss": "^4.1.16",
+    "@tailwindcss/vite": "^4.1.16"
+  }
+}