docs: add npm publish badges + global-install instructions

Now that v0.4.0 / v0.5.0 / v0.6.0 are live on the npm registry, surface
that in the README:

- npm version + monthly downloads badges (zh + en READMEs)
- new "全局安装" / "Global install" snippet alongside the existing NPX
  recipe — covers users who'd rather skip the npx prefix or work offline
- CHANGELOG Unreleased entry noting the registry publish

No code changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -6,6 +6,8 @@
 </p>
 
 <p align="center">
+  <a href="https://www.npmjs.com/package/master-skill"><img src="https://img.shields.io/npm/v/master-skill.svg?label=npm&color=cb3837" alt="npm version"></a>
+  <a href="https://www.npmjs.com/package/master-skill"><img src="https://img.shields.io/npm/dm/master-skill.svg?color=cb3837" alt="npm downloads"></a>
   <img src="https://img.shields.io/badge/License-MIT-blue.svg" alt="License: MIT">
   <img src="https://img.shields.io/badge/Python-3.9+-green.svg" alt="Python 3.9+">
   <img src="https://img.shields.io/badge/Claude%20Code-Skill-purple.svg" alt="Claude Code Skill">
@@ -124,7 +126,7 @@
 
 ### 安装
 
-**NPX 一键安装（推荐）**
+**NPX 一键安装（推荐，无需常驻）**
 
 ```bash
 # 安装指定祖师
@@ -137,6 +139,15 @@ npx master-skill install --all
 npx master-skill list
 ```
 
+**全局安装（频繁使用 / 离线场景）**
+
+```bash
+npm install -g master-skill            # 一次性装到 $PATH
+master-skill install master-zhiyi      # 之后省掉 npx，直接调
+master-skill list
+npm update -g master-skill             # 升到下一个 minor / patch
+```
+
 **Claude Code（插件方式）**
 
 ```bash