feat(web): split onboarding newsletter into its own third step

[elihahah666]

Why

onboarding 第二步「了解你」(About you) 同时塞了身份/规模/用途/来源四个调研下拉 和 newsletter 邮箱订阅，一屏里混了两类不相干的诉求，邮箱框被挤在问卷底部容易被忽略。把订阅单拎成独立的第三步，让 About-you 只做用户画像问卷、订阅有自己的落地步骤，转化路径更清楚。i18n key 和埋点枚举此前已为「第三步」预留，这次只是把 UI 接上。

What users will see

首次启动的 onboarding 引导从 2 步变 3 步：连接 → 了解你 → 获取最新动态。

• 第二步「了解你」只剩四个调研下拉，不再有邮箱框。
• 新增第三步「获取最新动态」(Stay in the loop)：一个占满面板宽度的可选邮箱订阅框，底部「上一步 / 完成设置」。
• 顶部步骤指示器相应变为三格，可点击来回切换。

行为不变：邮箱仍在最后一步点「完成设置」时提交；留空则跳过；只上报 opt-in 布尔，不上报邮箱地址本身。

Surface area

• UI — onboarding 新增独立的 newsletter 第三步 (apps/web)
• Keyboard shortcut
• CLI / env var
• API / contract
• Extension point
• i18n keys — 新增 settings.onboardingStepNewsletter（19 个 locale）
• New top-level dependency
• Default behavior change

说明 CLI 双轨：newsletter 订阅本身不是新 capability（既有功能），本 PR 仅在 onboarding UI 内重排步骤，未新增 /api 或 od 子命令，故 CLI 轨不适用。

Screenshots

第二步「了解你」(邮箱框已移出)：四个调研下拉 + 上一步/继续。
第三步「获取最新动态」：独立页面，占满宽度的邮箱框 + 上一步/完成设置；顶部三格步骤条第 3 格高亮。

(本地 headless 截图已核对：第三步邮箱框宽度 860px = 面板宽度，和第二步下拉框对齐。)

Bug fix verification

Validation

• pnpm guard ✅
• pnpm typecheck ✅
• pnpm --filter @open-design/web test ✅（324 文件 / 3184 用例通过，含更新后的 EntryShell.onboarding.test.tsx）
• 本地 pnpm tools-dev run web 起服务，headless 浏览器走完三步逐屏核对

[lefarcen]

Heads-up: PR #3651 (@Sid-Qin, "Make onboarding a focused setup flow") is also open and touches all four files this PR modifies — EntryShell.tsx, entry-layout.css, EntryShell.onboarding.test.tsx, and analytics/events.ts. #3651 is currently APPROVED but DIRTY against main. The two PRs will need a coordinated merge order to avoid conflicts — sharing so neither effort blocks the other.

[github-actions]

Visual regression review

Head: 8e92a0d · Base: e98e75f

10 changed · 25 unchanged · 0 missing baseline · 0 failed

Changed cases

Case	Main	PR	Diff
visual-avatar-local-agent-list
visual-avatar-menu
visual-home-plugin-use-with-query
visual-new-project-modal
visual-onboarding-runtime
visual-project-avatar-model-dropdown
visual-project-workspace
visual-settings-byok
visual-settings-execution
visual-settings-local-cli

Unchanged cases

Case	Main	PR	Diff
visual-design-system-detail
visual-design-systems
visual-home
visual-home-catalog
visual-home-context-picker
visual-home-plugin-filter
visual-home-plugin-use-staged
visual-home-staged-attachment
visual-integrations
visual-integrations-mcp
visual-integrations-use-everywhere
visual-plugin-details
visual-plugin-share-menu
visual-plugins
visual-projects
visual-projects-kanban
visual-settings-byok-model-dropdown
visual-settings-byok-openai
visual-settings-local-cli-model-dropdown
visual-tasks

Visual diff is advisory only and does not block merging.

[nettee]

I found one non-blocking analytics regression in the new onboarding step split: the About-you snapshot is now tied to a specific navigation action instead of the overall completion path.

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[Siri-Ray]

@elihahah666 thanks for splitting the newsletter capture into its own focused onboarding step. I found one merge-blocking issue: the PR adds the third step in the app and unit coverage, but the critical Playwright onboarding flows still exercise the old two-step path and are failing in CI.

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[nettee]

One non-blocking item remains in the current head: the e2e follow-up looks addressed, but the About-you analytics snapshot is still tied to one navigation path instead of the overall completion path.

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[elihahah666]

Thanks for the review — both points addressed:

@Siri-Ray (e2e P0 gate): Fixed in 09b1b96. e2e/ui/amr-onboarding.test.ts now clicks Continue from About you into the new Newsletter step before Finish setup, across every completion flow (AMR sign-in, BYOK, about-you, transient-recovery). Ran the full file locally — 10/10 passed.

@nettee (about_you_submit no longer exactly-once): Fixed in a361b3a. Moved the snapshot off the "leaving About-you" path back onto the completion path, stamped it with fixed About-you coordinates (area/step) since it describes the About-you submission regardless of which step finishes, and guarded it with a per-session aboutYouReportedRef so it fires exactly once. Added regression tests for both the forward stepper-jump and the Back-then-Continue detour flows.

Re-requesting review.