feat: add common config snippet management system

- Add settings module for managing common configuration snippets
- Implement UI for creating, editing, and deleting snippets
- Add tauri-plugin-fs for file operations
- Replace co-authored setting with flexible snippet system
- Enable users to define custom config snippets for frequently used settings

src-tauri/src/codex_config.rs

@@ -10,6 +10,10 @@ use std::path::Path;
 
 /// 获取 Codex 配置目录路径
 pub fn get_codex_config_dir() -> PathBuf {
+    if let Some(custom) = crate::settings::get_codex_override_dir() {
+        return custom;
+    }
+
     dirs::home_dir().expect("无法获取用户主目录").join(".codex")
 }