feat(R2)+refactor: 平台管理分区 + 删 3 桩页（档案80 #7）+ 无浏览器验收脚本

- R2：business-plugins 0.2.9 新增原生「平台管理」只读分区（已铺发到 admin/guest profile 并生效）
- 档案80 #7：删 web/{desktop,plugins,skills}.html（9→6 页）+ 5 处引用改直达 portal（nginx 已加 301）
- 新增 scripts/verify-platform-admin-section.mjs（打桩 react/jsx-runtime 真执行 client.js 做渲染断言）并接入 npm run verify

package.json

@@ -22,7 +22,7 @@
     "prepare": "npm run build",
     "dev": "node lib/cli.js",
     "typecheck": "tsc -p tsconfig.json --noEmit",
-    "verify": "npm run build && node --test test/db.test.mjs test/k8s-spawner.test.mjs test/leader.test.mjs test/local-user-fs.test.mjs test/crash-policy.test.mjs && node scripts/verify-inject.cjs lib/supervisor/proxy.js && node scripts/verify-static.mjs",
+    "verify": "npm run build && node --test test/db.test.mjs test/k8s-spawner.test.mjs test/leader.test.mjs test/local-user-fs.test.mjs test/crash-policy.test.mjs && node scripts/verify-inject.cjs lib/supervisor/proxy.js && node scripts/verify-static.mjs && node scripts/verify-platform-admin-section.mjs",
     "test": "npm run build && node --test test/db.test.mjs test/k8s-spawner.test.mjs test/leader.test.mjs test/local-user-fs.test.mjs test/crash-policy.test.mjs && node scripts/verify-inject.cjs lib/supervisor/proxy.js",
     "smoke": "node scripts/smoke.mjs",
     "smoke:admin": "node scripts/smoke-admin.mjs",