Add repository-wide AI guidance with AGENTS.md and internal custom agents #17054
Description
Is your feature request related to a problem? Please describe.
AI-assisted changes in the repository can be inconsistent because guidance is spread across different files and there is no single top-level agent workflow for planning, testing, implementation, migrations, changelog updates, and validation.
Describe the solution you'd like
Add a root AGENTS.md file for repository-wide agent guidance and introduce a set of internal custom agents for feature implementation and bug fixing Also align .github/copilot-instructions.md with the repository structure and modern Angular practices.
Additional context
This is intended to improve the consistency, predictability, and quality of AI-assisted contributions without changing production library behavior.