fix(ui): drop stale react-dom deps and address onboarding review

knip: ui-settings no longer imports react-dom (the portal moved into
OnboardingSurface), so the react-dom peer/dev dependencies and
@types/react-dom go away with the usage.

Review follow-ups: the Agent Note's Testing section now records the
held-join reload regression scenario this PR adds (both languages,
pairing re-recorded); the e2e hold gates EVERY settings.describe issued
before release instead of only the first, so a future boot-time join
consumer cannot silently collapse the widened window; the sampler's
persistence across later navigations is documented and the vacuity
wording softened to what the hold actually buys (timing independence).

.agents/notes/implemented/bug-fix/2026-08-06-onboarding-step-owned-takeover-chrome.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write .agents/notes/implemented/bug-fix/2026-08-06-onboarding-step-owned-takeover-chrome.md
-2026-08-06-onboarding-step-owned-takeover-chrome.md: 6f0b1fa5df95a7b82daaa50c147eb44f1c99e26c
-2026-08-06-onboarding-step-owned-takeover-chrome.zh.md: 37bbb47f6becf311d4a968bd47b48cce40051952
+2026-08-06-onboarding-step-owned-takeover-chrome.md: 4b3bbbc03c4494359297ae6e54bcc9a74c387e80
+2026-08-06-onboarding-step-owned-takeover-chrome.zh.md: 548285d285939325a26df3b8d70c43fe952813a9

.agents/notes/implemented/bug-fix/2026-08-06-onboarding-step-owned-takeover-chrome.md

@@ -32,4 +32,4 @@ A future step that registers without wrapping its visible content in `Onboarding
 
 ## Testing
 
-`packages/client/ui-primitives/tests/onboarding-surface.spec.tsx` pins the primitive: body portal around the content, mask/stage class presence, `#root` inert held for exactly the mount lifetime, and the no-`#root` composition. `packages/client/ui-settings/tests/settings-root.spec.tsx` pins the inverted shell contract: no takeover chrome and no inert while a mounted step renders nothing. The existing step specs (`ui-settings-general`, `ui-models`) and the assembled `apps/web/tests/onboarding-deepseek-config.e2e.ts` scenario continue to pass unchanged — the mask selector and geometry pins survive because the stylesheet moved verbatim.
+`packages/client/ui-primitives/tests/onboarding-surface.spec.tsx` pins the primitive: body portal around the content, mask/stage class presence, `#root` inert held for exactly the mount lifetime, and the no-`#root` composition. `packages/client/ui-settings/tests/settings-root.spec.tsx` pins the inverted shell contract: no takeover chrome and no inert while a mounted step renders nothing. `apps/web/tests/onboarding-deepseek-config.e2e.ts` gains the defect's assembled regression pin: a configured world reloads while every `settings.describe` response is held open at the browser's network boundary — widening the steps' deciding window from loopback-invisible to hundreds of milliseconds, which is what keeps the assertions non-vacuous — and an 8 ms in-page sampler proves the takeover chrome never mounts and `#root` never turns inert. The file's existing scenarios and the step specs (`ui-settings-general`, `ui-models`) pass unchanged — the mask selector and geometry pins survive because the stylesheet moved verbatim.

.agents/notes/implemented/bug-fix/2026-08-06-onboarding-step-owned-takeover-chrome.zh.md

@@ -32,4 +32,4 @@
 
 ## 测试
 
-`packages/client/ui-primitives/tests/onboarding-surface.spec.tsx` 钉住原语行为：内容外的 body portal、遮罩／展示层类名存在、`#root` 的 `inert` 恰好持续挂载生命周期，以及无 `#root` 的组合。`packages/client/ui-settings/tests/settings-root.spec.tsx` 钉住反转后的外壳契约：已挂载步骤什么都不渲染时，无接管界面框架、无 inert。既有的步骤 spec（`ui-settings-general`、`ui-models`）与整装的 `apps/web/tests/onboarding-deepseek-config.e2e.ts` 场景原样通过——样式表逐字迁移，遮罩选择器与几何钉子得以幸存。
+`packages/client/ui-primitives/tests/onboarding-surface.spec.tsx` 钉住原语行为：内容外的 body portal、遮罩／展示层类名存在、`#root` 的 `inert` 恰好持续挂载生命周期，以及无 `#root` 的组合。`packages/client/ui-settings/tests/settings-root.spec.tsx` 钉住反转后的外壳契约：已挂载步骤什么都不渲染时，无接管界面框架、无 inert。`apps/web/tests/onboarding-deepseek-config.e2e.ts` 新增本缺陷的整装回归钉：已配置世界刷新页面，同时在浏览器网络边界扣住所有 `settings.describe` 响应——把步骤的判定窗口从 loopback 下不可见拉宽到数百毫秒，这正是断言保持非空洞的关键——页内 8ms 采样器证明接管界面框架从未挂载、`#root` 从未变为 inert。该文件的既有场景与步骤 spec（`ui-settings-general`、`ui-models`）原样通过——样式表逐字迁移，遮罩选择器与几何钉子得以幸存。