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.md

@@ -4,7 +4,7 @@
 
 ### The All-in-One Manager for Claude Code, Codex, Gemini CLI, OpenCode & OpenClaw
 
-[![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)
@@ -126,7 +126,7 @@ Modern AI-powered coding relies on CLI tools like Claude Code, Codex, Gemini CLI
 
 ## Features
 
-[Full Changelog](CHANGELOG.md) | [Release Notes](docs/release-notes/v3.12.1-en.md)
+[Full Changelog](CHANGELOG.md) | [Release Notes](docs/release-notes/v3.12.3-en.md)
 
 ### Provider Management
 
@@ -211,6 +211,7 @@ Add an official provider from the preset list. After switching to it, run the Lo
 - **Local settings**: `~/.cc-switch/settings.json` (device-level UI preferences)
 - **Backups**: `~/.cc-switch/backups/` (auto-rotated, keeps 10 most recent)
 - **Skills**: `~/.cc-switch/skills/` (symlinked to corresponding apps by default)
+- **Skill Backups**: `~/.cc-switch/skill-backups/` (created automatically before uninstall, keeps 20 most recent)
 
 </details>