feat(skills): auto-backup skill files before uninstall

Create a local backup under ~/.cc-switch/skill-backups/ before removing
skill directories. The backup includes all skill files and a meta.json
with original skill metadata. Old backups are pruned to keep at most 20.
The backup path is returned to the frontend and shown in the success
toast. Bump version to 3.12.3.

README_ZH.md

@@ -4,7 +4,7 @@
 
 ### Claude Code、Codex、Gemini CLI、OpenCode 和 OpenClaw 的全方位管理工具
 
-[![Version](https://img.shields.io/badge/version-3.12.1-blue.svg)](https://github.com/farion1231/cc-switch/releases)
+[![Version](https://img.shields.io/badge/version-3.12.3-blue.svg)](https://github.com/farion1231/cc-switch/releases)
 [![Platform](https://img.shields.io/badge/platform-Windows%20%7C%20macOS%20%7C%20Linux-lightgrey.svg)](https://github.com/farion1231/cc-switch/releases)
 [![Built with Tauri](https://img.shields.io/badge/built%20with-Tauri%202-orange.svg)](https://tauri.app/)
 [![Downloads](https://img.shields.io/endpoint?url=https://api.pinstudios.net/api/badges/downloads/farion1231/cc-switch/total)](https://github.com/farion1231/cc-switch/releases/latest)
@@ -127,7 +127,7 @@ Claude Code / Codex / Gemini 官方渠道低至 3.8 / 0.2 / 0.9 折，充值更
 
 ## 功能特性
 
-[完整更新日志](CHANGELOG.md) | [发布说明](docs/release-notes/v3.12.1-zh.md)
+[完整更新日志](CHANGELOG.md) | [发布说明](docs/release-notes/v3.12.3-zh.md)
 
 ### 供应商管理
 
@@ -214,6 +214,7 @@ CC Switch 使用“通用配置片段”功能，在不同的供应商之间传
 - **本地设置**：`~/.cc-switch/settings.json`（设备级 UI 偏好设置）
 - **备份**：`~/.cc-switch/backups/`（自动轮换，保留最近 10 个）
 - **SKILLS**：`~/.cc-switch/skills/`（默认通过软链接连接到对应应用）
+- **技能备份**：`~/.cc-switch/skill-backups/`（卸载前自动创建，保留最近 20 个）
 
 </details>