refactor: skills 目录扁平化，移除分类子目录

- 将 00-元技能、01-AI工具、02-数据库、03-加密货币、04-开发工具、05-生产力 下的技能移至 skills/ 根目录
- 更新 skills/README.md 使用表格进行说明性分类
- 更新 AGENTS.md 目录结构说明

skills/ccxt/references/exchanges.md

@@ -0,0 +1,29 @@
+# Ccxt - Exchanges
+
+**Pages:** 2
+
+---
+
+## Search code, repositories, users, issues, pull requests...
+
+**URL:** https://github.com/ccxt/ccxt/wiki/Exchange-Markets
+
+**Contents:**
+- Supported Exchanges
+
+(If the page is not being rendered for you, you can refer to the mirror at https://docs.ccxt.com/)
+
+---
+
+## Search code, repositories, users, issues, pull requests...
+
+**URL:** https://github.com/ccxt/ccxt/wiki/Exchange-Markets-By-Country
+
+**Contents:**
+- Exchanges By Country
+
+The ccxt library currently supports the following cryptocurrency exchange markets and trading APIs:
+
+(If the page is not being rendered for you, you can refer to the mirror at https://docs.ccxt.com/)
+
+---