chore: Migrate CLAUDE.md to AGENTS.md (#217)

AS TITLE

---

**This PR was primarily authored with Codex using GPT-5-Codex and then
hand-reviewed by me. I AM responsible for every change made in this PR.
I aimed to keep it aligned with our goals, though I may have missed
minor issues. Please flag anything that feels off, I'll fix it
quickly.**

Signed-off-by: Xuanwo <[email protected]>

Author: Xuanwo

CLAUDE.md renamed to AGENTS.md

@@ -1,6 +1,6 @@
-# CLAUDE.md
+# AGENTS.md
 
-This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+This file provides guidance to AI coding agents when working with code in this repository.
 
 ## Project Overview
 
@@ -64,4 +64,4 @@ cargo fmt
 - Trait-based design for extensibility (`Backoff`, `Sleeper`, `Retryable`)
 - Feature-gated implementations for different platforms
 - Zero-cost abstractions with compile-time feature selection
-- No-std compatibility with optional std features
+- No-std compatibility with optional std features