docs(agents): simplify and consolidate AGENTS.md guidelines

Reduce file from 436 to 43 lines by removing redundant detailed documentation. Keep essential guidance and defer to monorepo root for comprehensive context.

Co-Authored-By: Hagicode <noreply@hagicode.com>
Signed-off-by: newbe36524 <newbe36524@qq.com>

Author: newbe36524