feat(keyboard): add English QuickType bar and system lexicon

Show verbatim/correction/completion slots, mmap a 40k-word list, and
use UITextChecker plus supplementary lexicon for conservative autocorrect.

CHANGELOG.md

@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **English QuickType bar**: while typing a word, three equal slots show the verbatim text (quoted when unknown), the unique Space correction, and a completion. The bar stays empty before typing and between committed words. / **英文 QuickType 栏**：输入单词时，三个等宽格显示原文（生词带引号）、空格会采用的唯一纠错和补全；尚未输入及单词提交后保持空白。
+- **System English lexicon**: typing uses `UITextChecker` completions/guesses and `requestSupplementaryLexicon` contact names / text replacements. / **系统英文词库**：打字使用 `UITextChecker` 补全/猜测，以及 `requestSupplementaryLexicon` 的通讯录名与文本替换。
+- **QWERTY proximity correction**: fat-finger substitutions on neighboring keys (for example `gppd` → `good`) outrank distant edit-distance neighbors. / **邻键纠错**：相邻键的胖手指替换（如 `gppd` → `good`）优先于远键编辑距离。
+- **Larger English word list**: about 40k unigrams and truncated bigrams, derived from Peter Norvig’s public-domain n-gram counts, shipped as an mmap binary so the keyboard extension does not parse them into Swift dictionaries. / **更大英文词表**：约 4 万 unigram 与截断 bigram，来自 Peter Norvig 公有领域 n-gram 计数，以 mmap 二进制随扩展加载，避免解析进 Swift 字典。
 - **Overlapping key presses**: the typing grid tracks multiple fingers, so the next key can go down before the previous lifts. Pending letters commit in press order (not release order); Shift can be held with one finger while another types. / **叠指连打**：打字网格跟踪多指，上一键未松开也可按下下一键。未提交的字母按按下顺序出字（而非抬手顺序）；一只手指按住 Shift 时另一只可打字。
 - **Period shortcut**: in English, a second Space shortly after a Space that follows a word becomes `. ` and arms sentence Shift, matching the system "." Shortcut. / **句号快捷**：英文下，在单词后的空格上短时间内再按一次空格会变成 `. ` 并点亮句首 Shift，对齐系统「句号快捷」。
 - **Return key labels**: Go / Search / Send / Done / Next / Join and the other `UIReturnKeyType` values show their system captions on the green action key instead of collapsing to Send or a return arrow. / **回车键文案**：前往 / 搜索 / 发送 / 完成 / 下一项 / 加入等 `UIReturnKeyType` 在绿色动作键上显示系统对应文案，不再一律变成「发送」或换行箭头。
@@ -17,9 +21,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Navigate skill**: copying text and tapping Navigate asks the LLM for one address (or origin → destination) and the host app opens driving directions — Amap if installed, then Baidu Maps, then Apple Maps. No companion Shortcut. No address stays in the current app with a keyboard tip. / **导航技能**：复制文字并点「导航」会抽取一条地址（或起点→终点），由 App 直接打开驾车导航——已装高德则用高德，否则百度，再否则 Apple 地图。不需要配套捷径。没有地址则留在当前 App，键盘上给出提示。
 - **Save to Notes skill**: the Skills tab opens a ready-made companion Shortcut named `OSGSaveToNotes` on the system Add page (one new Apple Note with an explicit title and body). After you tap Add, copying text and tapping Notes asks the LLM for a short title from the time and content; the body stays the original clipboard. / **存入备忘录技能**：技能页会打开已做好的配套捷径 `OSGSaveToNotes` 的系统添加页（新建一条带标题和正文的苹果备忘录）。点添加后，复制文字并点「备忘录」会按时间和内容生成短标题；正文保持剪贴板原文。
 - **Skills clipboard guide**: when Clipboard History is off, the Skills tab shows a card that jumps to in-app Clipboard settings and to iOS Settings for paste authorization. / **技能页剪贴板指引**：未开启剪贴板历史时，技能页展示可点击卡片，分别跳转 App 内剪贴板设置和系统设置以完成粘贴授权。
-- **Custom skills**: Skills tab `+` adds a user skill (name, about, SF Symbol, prompt, required iCloud Shortcut link with name lookup, independent Shortcut name, thinking off by default). Built-in thinking stays off and disabled. No cap on how many custom skills you can save; the keyboard still holds at most 8. / **自定义技能**：技能页右上角 `+` 可添加用户技能（名称、介绍、SF Symbol、提示词、必填 iCloud 捷径链接并自动读取名称、可与技能名分开的捷径名、思考默认关）。内置技能思考固定关闭且不可开。自定义数量不设上限，键盘仍最多启用 8 个。
+- **Custom skills**: Skills tab `+` adds a user skill (name, about, SF Symbol, prompt, optional iCloud Shortcut link with name lookup, independent Shortcut name, thinking off by default). Without a link, the model result is reviewed and inserted directly; with a link, it keeps the Shortcut export flow. Built-in thinking stays off and disabled. No cap on how many custom skills you can save; the keyboard still holds at most 8. / **自定义技能**：技能页右上角 `+` 可添加用户技能（名称、介绍、SF Symbol、提示词、可选 iCloud 捷径链接并自动读取名称、可与技能名分开的捷径名、思考默认关）。不填链接时，模型结果经确认后直接插入；填写链接时继续走捷径导出流程。内置技能思考固定关闭且不可开。自定义数量不设上限，键盘仍最多启用 8 个。
+
+### Changed
+- **Keyboard input tabs**: the four-tab capsule is centered independently of the side controls, with equal 42 pt hit widths and a translucent-black light-mode track. AI and Voice use enlarged `sparkle` and `waveform.mid` symbols, and the leading logo is 16 pt tall. / **键盘输入标签**：四标签胶囊不受两侧控件影响并在键盘上独立居中，点击宽度统一为 42 pt，浅色模式轨道使用半透明黑色；AI 与语音使用放大的 `sparkle` 和 `waveform.mid` 图标，左侧 Logo 高度为 16 pt。
+- **English lexicon mmap**: the 40k-word English table loads only in English and stays file-mapped; Chinese typing no longer pulls it in on keyboard appear. / **英文词表 mmap**：4 万词英文表仅在英文加载且走文件映射；中文打字不再在唤起键盘时一并灌入。
+- **English autocorrect conservatism**: Title Case / short / ALL CAPS tokens are not replaced, except same-length transpositions (`Teh` → `The`). Machine-applied corrections no longer boost the replacement; rejecting them learns the original. / **英文自动更正更克制**：Title Case / 短词 / 全大写默认不改，仅保留同长换位（`Teh` → `The`）。机器改写不再给新词加分；拒绝纠错会学会原文。
 
 ### Fixed
+- **Keyboard switch crash**: `requestSupplementaryLexicon` completion hops to the main actor before writing session state, so switching to OSG Keyboard no longer traps on `com.apple.TextInput.lexicon-request`. / **切换键盘崩溃**：`requestSupplementaryLexicon` 回调先回到主线程再写会话状态，切换到 OSG Keyboard 不再在 `com.apple.TextInput.lexicon-request` 上触发隔离断言。
 - **Save to Notes Shortcut**: bind the combined first-line title and clipboard body through iPhone Create Note’s real `WFCreateNoteInput` field. The previous `contents` binding was ignored and left an enter-content sheet or a title-only note. / **存入备忘录捷径**：通过 iPhone「创建备忘录」真正的 `WFCreateNoteInput` 字段绑定首行标题与剪贴板正文；旧版 `contents` 绑定会被忽略，导致弹出内容填写框或只生成标题。
 - **Extract tasks Shortcut**: receive Shortcut Input as Text, then split lines and add each title to Reminders — the previous recipe could finish successfully without creating items. / **提取待办捷径**：先把快捷指令输入收成文本，再按行写入提醒；旧配方会成功跑完但不创建条目。
 - **Skill reorder feedback**: long-press lifts a skill card and the grid slides live under the finger, matching Home Screen rearrange. / **技能拖动排序**：长按拎起技能卡片，网格随手指实时让位，接近主屏幕图标重排。