refactor(archive): remove archive on provider switches/updates

- Remove file archiving when switching providers or updating current provider
- Keep archive functionality only for initial migration (one-time operation)
- Retain simple .bak backup for config.json on each save
- Simplify code by removing unnecessary archive operations from daily workflows

This change prevents unlimited archive growth while maintaining data safety through:
1. Initial migration archives for historical data preservation
2. Single .bak file for basic rollback capability
3. All provider configs stored in SSOT (config.json)

src-tauri/src/app_config.rs

@@ -107,7 +107,16 @@ impl MultiAppConfig {
     /// 保存配置到文件
     pub fn save(&self) -> Result<(), String> {
         let config_path = get_app_config_path();
-        write_json_file(&config_path, self)
+        // 先备份旧版（若存在）到 ~/.cc-switch/config.json.bak，再写入新内容
+        if config_path.exists() {
+            let backup_path = get_app_config_dir().join("config.json.bak");
+            if let Err(e) = copy_file(&config_path, &backup_path) {
+                log::warn!("备份 config.json 到 .bak 失败: {}", e);
+            }
+        }
+
+        write_json_file(&config_path, self)?;
+        Ok(())
     }
 
     /// 获取指定应用的管理器