Allow creating agent materials local to a repository

[local-materials-conversation-summary.md](https://github.com/user-attachments/files/28576053/local-materials-conversation-summary.md)

[local.md](https://github.com/user-attachments/files/28575969/local.md)

[local-v2.md](https://github.com/user-attachments/files/28575971/local-v2.md)