chore: 版本号 0.1.0 → 0.9.0-beta.1 + updater 插件预留

- package.json / tauri.conf.json: version 更新为 0.9.0-beta.1
- tauri.conf.json: 添加 plugins.updater 空壳配置 + createUpdaterArtifacts
- Cargo.toml: 添加 tauri-plugin-updater 依赖
- lib.rs: 注册 updater 插件 (空壳，部署时配置 HTTPS 端点 + Ed25519 密钥)

desktop/src-tauri/src/lib.rs

@@ -147,7 +147,8 @@ pub fn run() {
     let classroom_gen_tasks = classroom_commands::create_generation_tasks();
 
     let mut builder = tauri::Builder::default()
-        .plugin(tauri_plugin_opener::init());
+        .plugin(tauri_plugin_opener::init())
+        .plugin(tauri_plugin_updater::Builder::new().build());
 
     // MCP debug plugin — only in debug builds, allows AI agents to interact with the app
     #[cfg(debug_assertions)]