docs(whitepaper): track PDF via Git LFS and link it in READMEs

.gitattributes

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+*.pdf filter=lfs diff=lfs merge=lfs -text

README.CN.md

@@ -24,6 +24,8 @@ Distillation）等误差缓解技术。其模块化设计支持独立使用各
 
 了解更多请访问 **[qc.zdxlz.com/cqlib](https://qc.zdxlz.com/cqlib)**。
 
+**[阅读白皮书](docs/whitepaper/Cqlib.pdf)** —— 一份文档讲清 Cqlib 的设计理念、系统架构与技术细节。
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 ## 核心特性
 
 - **量子线路构建** — 直观的 API 用于构建、组合和参数化量子线路

README.md

@@ -28,6 +28,8 @@ education, and integration into larger software stacks.
 
 Learn more at **[qc.zdxlz.com/cqlib](https://qc.zdxlz.com/cqlib)**.
 
+**[Read the Whitepaper](docs/whitepaper/Cqlib.pdf)** — Cqlib's design philosophy, architecture, and technical details in one document.
+
 ## Features
 
 - **Circuit Construction** — Intuitive APIs to build, compose, and parameterize quantum circuits