feat(i18n): add English and Simplified Chinese localization

[squarepots]

中文

实现状态

本 PR 完成 Codex Switcher 的双语本地化基础，并基于最终依赖栈 #180、#182、#185、#184、#186 和 #183 完成整合。

• 桌面语言偏好由 AppSettings.ui_language_preference 作为唯一持久化 authority，支持 System default、English、简体中文；解析后的 en-US / zh-CN 同步到主窗口、托盘 webview、原生应用菜单和原生托盘菜单。
• 浏览器语言偏好只属于当前浏览器，支持 Browser default、English、简体中文。当前 JS session 的 in-memory preference 是唯一 semantic authority；localStorage 只做尽力持久化。显式选择先更新内存，即使 storage 不可用，React、设置 picker 和 web-secret prompt 也保持一致；Browser default 才按 navigator.languages 的第一个受支持语言解析，且不会写入桌面设置。
• Desktop 安装身份只由 initialize_app_settings() 决定：新安装持久化 System，已有 pre-localization 安装及缺少语言字段的 legacy settings 持久化 English，显式偏好和 legacy language 字段保持不变。普通 runtime read 只读取 AppSettings；缺失 settings 时固定使用 English safe fallback，绝不再依据 accounts.json 重新推断语言。设置写入继续复用 locked/atomic persistence。
• 明确区分简体与繁体环境，覆盖 zh-CN、zh_CN、zh-Hans、zh-Hans-*、zh-SG，并让 zh-TW、zh-HK、zh-MO、zh-Hant*、裸 zh 回退到 English。
• 使用显式 React render-time translation、双 JSON catalog、已迁移 surfaces 的语义化文案和 i18next 插值/复数；不使用 DOM observer 或 DOM 重写。
• 原生应用菜单和托盘菜单使用稳定的语义化 native text keys，再由统一映射提供英文与简体中文，避免把英文显示文案当作状态标识。
• 补齐设置、备份、浏览器 secret、强制关闭、reset credits、usage stats、可访问名称和 native surface 文案；保持原始账号、错误、路径、provider 值及日期/数字/时区格式不变。
• 语言写入成功后返回 authoritative DisplaySettings，先尽力投影 native menu/tray，再通过现有 app-settings-changed 机制通知 webview；投影失败不会伪报持久化失败。
• 初始化与读取失败只记录日志，不阻塞 Desktop 启动；原生应用菜单、托盘和 React 首屏使用 English safe fallback，并可在 storage 恢复后通过既有 settings 流程 reconciliation。document.documentElement.lang 仅是已解析语言的 projection，不是 browser authority。
• 分支按最终依赖栈 fix(web): bound request concurrency #180（597b970）、fix(storage): make state writes atomic and single-writer #182（2fadfc7）、fix(auth): align OAuth refresh policy with Codex #185（7aa083b）、fix(auth): make activation a single transaction #184（5a606f6）、feat(warmup): persist host-owned scheduling policy #186（c66cc5e）和 feat(backup): add user-passphrase encryption #183（d52e172）验证，保留 web boundary、passphrase backup、auth transaction、OAuth refresh 和 Rust-owned warm-up scheduler 的既有行为。

验证

• pnpm test:i18n：8 项通过
• pnpm test:desktop-reopen：7 项通过
• pnpm test:browser-runtime：2 项通过
• pnpm test:close-preference：3 项通过
• pnpm test:reset-credits：3 项通过
• pnpm test:warmup-policy：1 项通过
• pnpm test:web-boundary：1 项通过
• pnpm test:backup-passphrase：3 项通过
• pnpm build：通过
• cargo fmt --manifest-path src-tauri/Cargo.toml --all -- --check：通过
• cargo check --locked --manifest-path src-tauri/Cargo.toml：通过
• cargo test --locked --manifest-path src-tauri/Cargo.toml：101 项通过
• git diff --check：通过

Closes #157

---

English

Implementation status

This PR completes the bilingual localization foundation for Codex Switcher on the final dependency stack: #180, #182, #185, #184, #186, and #183.

• Desktop language preference has one persisted authority, AppSettings.ui_language_preference, with System default, English, and 简体中文. The resolved en-US / zh-CN language is projected to the main window, tray webview, native application menu, and native tray menu.
• Browser language preference belongs only to the current browser, with Browser default, English, and 简体中文. The current JS session in-memory preference is the single semantic authority; localStorage is best-effort persistence only. Explicit choices update memory first, so React, the settings picker, and the web-secret prompt stay aligned even when storage is unavailable. Only Browser default resolves the first supported entry from navigator.languages, and it never writes desktop settings.
• Desktop installation identity is decided only by initialize_app_settings(): new installs persist System; existing pre-localization installs and legacy settings without language persist English; explicit preferences and the legacy language field survive. Ordinary runtime reads only read AppSettings; a missing settings file always uses the English safe fallback and never re-infers language from accounts.json. Settings writes reuse locked/atomic persistence.
• Simplified and Traditional Chinese are separated. The resolver covers zh-CN, zh_CN, zh-Hans, zh-Hans-*, and zh-SG; zh-TW, zh-HK, zh-MO, zh-Hant*, and bare zh fall back to English.
• Translation uses explicit React render-time rendering, two JSON catalogs, semantic copy for the migrated surfaces, and i18next interpolation/pluralization. No DOM observer or DOM rewrite is used.
• Native application and tray menus use stable semantic text keys mapped to English and Simplified Chinese, so translated display strings never become program state.
• Settings, backup, browser-secret, force-close, reset-credit, usage-statistics, accessibility, and native-surface copy is localized. Raw account, error, path, provider, date, number, and timezone semantics remain unchanged.
• Successful language writes return authoritative DisplaySettings, attempt native menu/tray projection before notifying webviews through the existing app-settings-changed mechanism, and do not report persistence failure when a projection fails.
• Initialization and read failures are logged without blocking Desktop startup; native menus, the tray, and the React first screen use the English safe fallback and can reconcile through the existing settings flow when storage becomes usable. document.documentElement.lang is only a projection of the resolved language, never browser authority.
• The branch was verified against the final dependency stack: fix(web): bound request concurrency #180 (597b970), fix(storage): make state writes atomic and single-writer #182 (2fadfc7), fix(auth): align OAuth refresh policy with Codex #185 (7aa083b), fix(auth): make activation a single transaction #184 (5a606f6), feat(warmup): persist host-owned scheduling policy #186 (c66cc5e), and feat(backup): add user-passphrase encryption #183 (d52e172), preserving the existing web boundary, passphrase backup, auth transaction, OAuth refresh, and Rust-owned warm-up scheduler behavior.

Validation

• pnpm test:i18n: 8 passed
• pnpm test:desktop-reopen: 7 passed
• pnpm test:browser-runtime: 2 passed
• pnpm test:close-preference: 3 passed
• pnpm test:reset-credits: 3 passed
• pnpm test:warmup-policy: 1 passed
• pnpm test:web-boundary: 1 passed
• pnpm test:backup-passphrase: 3 passed
• pnpm build: passed
• cargo fmt --manifest-path src-tauri/Cargo.toml --all -- --check: passed
• cargo check --locked --manifest-path src-tauri/Cargo.toml: passed
• cargo test --locked --manifest-path src-tauri/Cargo.toml: 101 passed
• git diff --check: passed

Closes #157

Restores #168 after the source fork was accidentally deleted.

---

Maintenance triage — 2026-09-30

Prerequisite PRs: #178, #180, #182, #185, #184, #186, #183.