Inline the AI policy's core principles in AGENTS.md

A bare link is easy for agents to skip (no fetch happens). State the checkable requirements directly so the file works even when the policy page is never opened; the link remains the full reference.

Co-authored-by: Muse Code (Meta Muse Spark)

Author: ambv

AGENTS.md

@@ -6,3 +6,11 @@ must follow it.
 
 > [!important]
 > **Primary directive**: Read the policy before making or proposing any changes.
+
+When acting on this repository, apply the policy's core principles:
+
+- Consider whether the change is necessary.
+- Make minimal, focused changes.
+- Follow existing coding style and patterns.
+- Write tests that exercise the change.
+- Keep backwards compatibility with prior releases in mind.