perf(keyboard): track KeyboardState per property with @Observable

- KeyboardState moves from ObservableObject/@Published to @Observable, so a view re-renders only for the properties it reads. Previously unpublished state and injected action hooks are @ObservationIgnored.
- KeyboardViewController replaces the $phase/$surface Combine sinks with Observations loops tied to the same cancellables.
- AIKeyboardView reads the 200 ms mic level and live ASR partials in small child views (AssistantWaveform, LiveTranscriptReader), so those ticks no longer rebuild the whole assistant surface.
- Tests observe changes with withObservationTracking instead of Combine publishers.

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Messaging shift to AI voice keyboard / voice double / agentic skills**: README and the product page now lead with “Say it. It’s typed. Speaks like you. Acts for you.” — the personalization story (learned style, three-tone replies) moves ahead of typing, clipboard skills are framed as agentic actions, and typing becomes the fallback capability. / **宣传定位转向 AI 语音键盘 / 嘴替 / Agentic 技能**：README 与产品页改用「开口即文字。会说你的话，会办你的事。」定位；个人化卖点（专属风格、三语气回复）提前，剪贴板技能表述升级为 Agentic 行动，打字退为兜底能力。
 - **Product page redesign**: rebuild the GitHub Pages home as a dark product stage with the new Icon Composer app icon, the three-device hero visual, and real on-device videos and UI cards replacing hand-drawn mockups; add 2.1 selling points (personal style, three-tone replies, monthly usage calendar, EventKit skills export, guided trials and credit rewards), a TestFlight link, and self-hosted inline SVG icons; bump page references to 2.1.0. / **产品页重设计**：GitHub Pages 主页改为深色产品舞台，启用 Icon Composer 新图标与三端同框主视觉，以实机视频与真实界面卡片取代手绘示意；补齐 2.1 卖点（专属风格、三语气个性回复、月度用量日历、EventKit 技能写入、引导体验与积分奖励），新增 TestFlight 入口，图标改为自托管内联 SVG；页面版本号更新至 2.1.0。
 - **Host-only analytics recording**: the keyboard extension no longer opens the analytics or keyboard-usage SQLite queues. The host app is the only process that records and uploads events, so hiding the keyboard cannot hold WAL locks and get killed as `0xdead10cc`. Keyboard-activated and per-keystroke usage events are no longer collected. / **仅主 App 记埋点**：键盘扩展不再打开统计与键盘用量 SQLite 队列；开库、记账与上传只在主 App 进行，收起键盘时不会因 WAL 锁被系统以 `0xdead10cc` 终止。不再采集「键盘激活」和逐次按键用量。
+- **Lighter keyboard redraws while dictating**: the keyboard now redraws only the parts whose data changed. The microphone level (5 times a second) updates just the waveform bars, and live recognized text updates just the status line, instead of rebuilding the whole voice panel each time. / **听写时键盘重绘更轻**：键盘现在只重绘数据有变化的部分。麦克风音量（每秒 5 次）只刷新波形条，实时识别文字只刷新状态行，不再每次都重建整个语音面板。
 
 ### Fixed
 - **Keyboard killed after hiding on pinyin**: hiding the keyboard while the pinyin/English typing surface was showing kept librime's user dictionary open, and its LevelDB `LOCK` file in the shared App Group got the suspended extension killed as `0xdead10cc` (about 30 kills in 3 days on one test device). The typing engine is now closed on every hide and reopened on the next show, which adds about 30–50 ms only when a still-running keyboard is reopened. / **拼音界面收起后键盘被系统终止**：在拼音/英文打字界面收起键盘时，librime 用户词库仍保持打开，其位于共享 App Group 的 LevelDB `LOCK` 文件导致挂起的扩展被系统以 `0xdead10cc` 终止（一台测试机 3 天约 30 次）。现在每次收起都会关闭打字引擎、下次弹出时重新打开，仅在复用仍存活的键盘进程时多约 30–50 毫秒。