fix(web): 首页只留下载、去登录/在线体验入口; 下载区改二维码; 修复网络版一直提示新版本

- Landing: 移除 header 登录/进入应用按钮、hero 在线体验入口
- 下载区: 复制链接行改为 qrcode.react 二维码 (扫码下载 APK)
- 修复 '持续提示新版本可用' bug: vite 构建时把 BUILD_ID 写入 dist/.build-id,
  manifest-web 返回当前部署 dist 的 build_id, 与浏览器内置值同源比对;
  此前返回 OTA 包 build_id (seq-<ts>) 与页面 BUILD_ID 永不一致 → 横幅常驻

package-lock.json

@@ -13,6 +13,7 @@
         "cors": "^2.8.5",
         "dotenv": "^16.4.5",
         "express": "^4.21.2",
+        "qrcode.react": "^4.2.0",
         "react": "^18.3.1",
         "react-dom": "^18.3.1",
         "react-router-dom": "^6.26.0",
@@ -3473,6 +3474,15 @@
         "node": ">=6"
       }
     },
+    "node_modules/qrcode.react": {
+      "version": "4.2.0",
+      "resolved": "https://registry.npmjs.org/qrcode.react/-/qrcode.react-4.2.0.tgz",
+      "integrity": "sha512-QpgqWi8rD9DsS9EP3z7BT+5lY5SFhsqGjpgW5DY/i3mK4M9DTBNz3ErMi8BWYEfI3L0d8GIbGmcdFAS1uIRGjA==",
+      "license": "ISC",
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      }
+    },
     "node_modules/qs": {
       "version": "6.15.3",
       "license": "BSD-3-Clause",