fix: 修复 plugin_type 使用无效的 builtin 值

将 plugin_type 从 builtin 改为 script，修复安装时报错：
"unknown variant `builtin`, expected one of `lua`, `script`, `native`, `binary`"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: wutongci

plugin/plugin.json

@@ -1,9 +1,9 @@
 {
   "name": "config-switch",
-  "version": "0.1.0",
+  "version": "0.1.1",
   "description": "Config Switch - 一键切换 API 配置，支持 Claude Code、Codex、Gemini 等客户端",
   "author": "ProxyCast Team",
-  "plugin_type": "builtin",
+  "plugin_type": "script",
   "min_proxycast_version": "1.0.0",
   "ui": {
     "surfaces": ["tools", "sidebar"],