docs: add online demo section linking to fojin.app/chat

Users can now try all pre-built masters directly in the browser
without installing Claude Code or Codex CLI.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -43,6 +43,14 @@
 
 ---
 
+## 在线体验
+
+无需安装任何工具，直接在浏览器中体验所有预置法师：
+
+**[fojin.app/chat](https://fojin.app/chat)** — 打开 AI 问答页面，左下角「法师模式」选择祖师即可开始对话。
+
+---
+
 ## 声明
 
 本项目本着对佛教传统的尊重而建立。所有内容均依据佛教经典文献生成，不做教义评判，不代表任何宗派权威。生成内容仅供学习参考，如需正式修行指导，请亲近善知识。

README_EN.md

@@ -52,6 +52,14 @@ This project is built out of respect for Buddhist traditions. All content is gen
 
 ---
 
+## Online Demo
+
+No installation required — try all pre-built masters directly in your browser:
+
+**[fojin.app/chat](https://fojin.app/chat)** — Open the AI Q&A page, select a master from the "法师模式" dropdown (bottom-left), and start chatting.
+
+---
+
 ## Features
 
 - **8 pre-built Chinese Buddhist masters**: across Yogacara, Madhyamaka, Chan, Tiantai, Huayan, Pure Land, and cross-tradition — ready to use out of the box