[Feature Request] Move `.github/copilot-instructions.md` to `AGENTS.md`

### Summary Move `.github/copilot-instructions.md` to `AGENTS.md` since the latter is common used by different agents. ### Detailed Description As above. ### Further Information, Files, and Links https://github.blog/changelog/2025-08-28-copilot-coding-agent-now-supports-agents-md-custom-instructions/