docs(site): replace CSS blobs with liquid aurora WebGL

Upgrade the hero background to a domain-warped FBM fluid shader with
theme palettes, dithering, soft pointer pull, and motion-safe fallbacks.

CHANGELOG.md

@@ -8,7 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
-- **Hero aurora background**: soft animated green/teal/violet aurora wash on the marketing site hero, with reduced-motion static fallback. / **Hero 极光背景**：官网首屏加入缓慢漂移的绿/青/紫极光柔光，并在减少动态模式下退回静态。
+- **Liquid aurora hero**: WebGL2 domain-warped FBM shader — slow green/teal/violet fluid, dithering, pointer pull, offscreen pause, and reduced-motion static frame (CSS gradient fallback). / **液态极光 Hero**：WebGL2 domain-warped FBM 着色器——缓慢绿/青/紫流体、抖动去色带、轻微指针牵引、离屏暂停、减少动态模式下静态帧（CSS 渐变回退）。
 - **App Store download badges**: official badges on bilingual READMEs (hero + Get sections) and the website, with China-store `/cn/` links for Chinese and regionless App Store links for English. / **App Store 下载徽章**：中英文 README（顶部与获取区）与官网挂载官方徽章；中文链 `/cn/`，英文用无地区链接。
 - **Website SEO & AI discovery**: richer meta/JSON-LD/FAQ, `llms.txt`, expanded sitemap, English landing, plus install / compare / Mac-dictation content pages. / **官网 SEO 与 AI 发现**：强化 meta/JSON-LD/FAQ、`llms.txt`、sitemap，并新增英文落地页与安装 / 对比 / Mac 听写专题页。
 - **Context-aware polish safeguards**: polish can use a redacted cursor-neighborhood snapshot for natural continuation, validates protected terms and identifiers, retries once, and falls back to a conservative local cleanup when needed. / **上下文润色护栏**：润色可使用经截断脱敏的光标附近文字自然衔接，并校验受保护词与标识符；失败时重试一次，仍不合格则降级为本地保守清理。