refactor: 重构目录结构以支持 i18n

创建 'i18n' 目录以存放多语言内容。将所有现有的中文内容（文档、提示词、技能、README）移动到 'i18n/zh/' 中。添加了新的根 README 作为语言入口，并为英文（'en'）翻译创建了占位符结构。

skills/cryptofeed/references/index.md

@@ -1,24 +0,0 @@
-# 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)