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/cryptofeed/references/index.md

@@ -0,0 +1,24 @@
+# Cryptofeed Documentation Index
+
+## Categories
+
+### README
+**File:** `README.md`
+**Pages:** 1 (192 lines)
+
+Complete overview of Cryptofeed including:
+- Installation instructions
+- Supported exchanges (40+)
+- Basic usage examples
+- NBBO (National Best Bid/Offer) implementation
+- Supported channels and backends
+- REST API information
+
+## Quick Links
+
+- Installation and setup → `README.md`
+- Basic usage examples → `README.md` (line 52-76)
+- NBBO example → `README.md` (line 83-100)
+- Supported exchanges → `README.md` (line 9-50)
+- Data channels → `README.md` (line 102-125)
+- Backend integrations → `README.md` (line 127-146)