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

* Initial plan

* Add comprehensive agents.md file for repository documentation

Co-authored-by: BornToBeRoot <[email protected]>

* Chore: Adjust agents md

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: BornToBeRoot <[email protected]>

Author: Copilot