docs(license): state AGPL-3.0 in the READMEs, matching the LICENSE file

LICENSE became AGPL-3.0-only in 037eb24, but both READMEs still told readers
the project was MIT — the one place a user actually looks before deciding what
they may do with it. The two "license notes" underneath were MIT-shaped as
well: attribution and a disclaimer, with no mention of copyleft at all.

They now say what AGPL actually requires, including section 13, which is the
clause that matters most here: Felis is a hosting platform reached over a
network, so a modified deployment owes its source to the people using it even
if no binary is ever distributed. Leaving that unsaid was the part that could
mislead someone into a violation they never intended.

README.md

@@ -70,12 +70,13 @@ docker build -t felis:custom .
 
 ## 开源协议
 
-本项目代码部分遵循 MIT License 开源协议。
+本项目遵循 [AGPL-3.0-only](LICENSE) 开源协议。
 
 ### 协议注意事项
 
-1. **保留版权声明**：在您分发本项目的副本或基于本项目衍生的软件中，必须包含原作者的版权声明和许可声明。
-2. **免责声明**：本项目按"原样"提供，作者不承担任何因使用本项目而产生的法律责任。
+1. **衍生作品同样是 AGPL**：分发本项目的副本或基于本项目衍生的软件时，必须以 AGPL-3.0 开源，并保留原作者的版权声明和许可声明。
+2. **通过网络提供服务同样要开源**（AGPL 第 13 条）：如果你把修改过的 Felis 架起来给别人用，即使从不分发任何二进制，也必须向这些用户提供你那份修改后的完整源码。这是 AGPL 相对 GPL 的唯一实质区别，而 Felis 正是一个跑在网络上的托管平台，所以这一条基本总会触发。
+3. **免责声明**：本项目按"原样"提供，作者不承担任何因使用本项目而产生的法律责任。
 
 ## 致谢