Add agents.md repository guide for AI agents (#3266)

* Initial plan

* Add comprehensive agents.md file for repository documentation

Co-authored-by: BornToBeRoot <16019165+BornToBeRoot@users.noreply.github.com>

* Chore: Adjust agents md

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: BornToBeRoot <16019165+BornToBeRoot@users.noreply.github.com>

Author: Copilot