fix(nav): add in-app back button and prevent LAST_DOC_ID from drifting on every navigation

[sun-970]

Summary

• Add in-app back button to the TopBar (ArrowLeft icon next to Logo) that calls window.history.back(). The button only appears after the first in-app navigation to avoid confusion on direct page load.
• Fix LAST_DOC_ID persistence using sessionStorage to track whether we've recorded the entry doc. This properly scopes the flag to the page session — survives SPA navigation but resets on full page reload.
• Add i18n keys for the back button label (goBack) in zh-cn.json and en.json.

Test plan

• npx vitest run — all tests pass
• npx tsc --noEmit — no TypeScript errors
• Back button is hidden on direct page load
• Back button appears after in-app navigation and works correctly
• LAST_DOC_ID is written only on first doc load per session
• "Get Started" button returns to the entry doc after in-session navigation

Note

This PR depends on #65 (i18n base). Should be rebased after #65 is merged.

Closes: #66

[PeterGuy326]

REQUEST CHANGES\n\n1. src/app/[locale]/work/[id]/(content)/content-for-my-doc.tsx:22-42 使用模块级可变变量 hasRecordedEntryDoc，但注释称它是 page session。这个 flag 会跟随浏览器 bundle 跨组件挂载、同一 SPA 中离开文档页再进入另一篇文档，以及 HMR 生命周期持续，实际不是一次页面会话；在 SSR/预渲染或模块复用场景也需要确认不会提前消耗。请改为组件实例或明确的页面会话状态，并补充首次进入、离开后再次进入、侧边栏切换的回归测试。\n\n2. src/app/[locale]/work/[id]/top-bar.tsx:42-47 返回按钮无可退历史判断。首次直接打开文档时按钮仍显示，点击会退到站外页面或无效果。请基于现有 pushState/popstate 记录判断是否存在应用内历史，没有时隐藏或 disabled，并补充 direct-load 与 in-app navigation 的手工/自动验证。\n\n验证：PR head 33cffac 已在本地核对，npx vitest run src/tests/lib/dt.test.ts 通过，3 tests；GitHub CI 当前全绿，但 PR 描述中的 4 个导航手工场景仍未完成，本次 diff 也没有 CHANGELOG.md 的 [Unreleased] 条目。\n\n跨 PR：#67 当前包含 #65 的 commit b3f1749，并改动相同的 i18n 文件。建议先合并并稳定 #65，再让 #67 基于 #65 重放/去重后复审，避免把两个 PR 的基础改动和冲突混在一起。

[PeterGuy326]

复核当前 head 34e7867：模块级 flag 已改为 sessionStorage，返回按钮也已加应用内历史判断，现有 CI 全绿；本次先不 APPROVE，剩余门禁仍未闭环：PR 描述还写着 module-level flag，307 测试数和手工验证清单未更新/未勾选，本次 diff 仍没有 CHANGELOG.md 的 [Unreleased] 条目；同时该分支仍包含 #65 的基础提交，建议 #65 稳定后 rebase/去重再 request re-review。

[waterbro-8]

Review

CI: test and docker-build pass.

The back button + LAST_DOC_ID session flag address the chromeless-container stranding in #66. Using existing pushState/popstate is the right mechanism.

Must fix

1. This PR also contains #65. timeAgo i18n, version createdAt ISO, version-dialog locale formatting, and dt.ts changes duplicate #65. That will conflict on merge and makes review/revert messy. Please drop those files from this branch and leave them on #65.
2. src/lib/dt.ts imports useTranslations and adds useTimeAgo. If any leftover i18n stays here, a React hook inside a shared date lib is easy to call from a server module. Prefer keeping hooks out of dt.ts.

Gaps vs #66 (non-blocking if you update the issue)

• No ancestor breadcrumb.
• No in-app “reset entry point” control (issue AC). sessionStorage flag is undocumented.
• Back button only appears after an in-app EVENT_KEY_NAV_DOC; a deep link still has no way back.

Verdict: request changes — strip the #65 overlap, then this is mergeable for the back-button slice.

[sun-970]

Changes pushed: stripped #65 overlap (rebased onto main), CHANGELOG entry added, CI green. Ready for re-review.

[waterbro-8]

Re-review

Previous must-fixes look done on the current head:

• #65 overlap is gone (this diff is TopBar + entry-doc flag + i18n goBack + CHANGELOG only)
• module-level flag replaced with sessionStorage
• back button is gated on in-app EVENT_KEY_NAV_DOC
• CHANGELOG [Unreleased] is present
• CI is green

Residual (non-blocking)

• hasRecordedEntryDoc is a magic string; match LAST_DOC_ID_KEY and keep it in constants.
• Still no automated test for direct-load vs in-app navigation. Manual checklist in the PR body is the only coverage.
• history.back() after EVENT_KEY_NAV_DOC is enough for the chromeless-container slice. Ancestor breadcrumb and an explicit “reset entry” control from #66 remain out of this PR.

Verdict: approve for the back-button / entry-doc slice.

[PeterGuy326]

Reviewed current head 8654fb2.

• The previously requested module-level flag change is now sessionStorage-scoped.
• The back button is gated by the in-app EVENT_KEY_NAV_DOC navigation event, so direct loads do not expose it.
• The #65 overlap is gone from the current diff; only the back-button/entry-doc slice, locale labels, and CHANGELOG entry remain.
• Required CI is green: test, docker-build, dependency review, and Scorecard.
• Existing CODEOWNER approval is present.

Residuals are non-blocking for this slice: the sessionStorage key could be centralized, and navigation behavior is covered by the documented manual checklist rather than an automated regression. Because this PR depends on #65, rebase or otherwise verify the final merge result after #65 lands.

[waterbro-8]

#65 已合入 main（3bd2e27）。这个 PR 现在与 main 冲突（多半是 CHANGELOG）。我推不了 sun-970/doc，请 rebase 到当前 main 后再 push。

[Bindy-lbb]

LGTM. Clean approach: entry doc recorded once per session via sessionStorage gate, back button gated on emitter-tracked in-app navigation so it only appears after a genuine SPA transition. i18n keys present for both locales. No concerns.

[PeterGuy326]

@sun-970 #65 已合入 main，现在 #67 与最新 main 冲突，GitHub 自动 rebase 无法自动处理

我这边没有 sun-970/doc 的 push 权限，麻烦你把当前分支 rebase 到 bytefolk/doc/main 后 force-with-lease 推回，CHANGELOG 里的两个 Unreleased 条目都保留

推好后告诉我，我继续合 #67 和 #69
#67