feat(config): backup v1 file before v2 migration

- Add timestamped backup at `~/.cc-switch/config.v1.backup.<ts>.json`
- Keep provider files untouched; only cc-switch metadata is backed up
- Remove UI notification plan; backup only as requested
- Update CHANGELOG with migration backup notes

CHANGELOG.md

@@ -44,6 +44,11 @@ For users upgrading from v2.x (Electron version):
 - The app will automatically migrate your existing provider configurations
 - Window position and size preferences have been reset to defaults
 
+#### Backup on v1→v2 Migration (cc-switch internal config)
+- When the app detects an old v1 config structure at `~/.cc-switch/config.json`, it now creates a timestamped backup before writing the new v2 structure.
+- Backup location: `~/.cc-switch/config.v1.backup.<timestamp>.json`
+- This only concerns cc-switch's own metadata file; your actual provider files under `~/.claude/` and `~/.codex/` are untouched.
+
 ### 🛠️ Development
 - Added `pnpm typecheck` command for TypeScript validation
 - Added `pnpm format` and `pnpm format:check` for code formatting

src-tauri/src/app_config.rs

@@ -1,7 +1,7 @@
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 
-use crate::config::{get_app_config_path, write_json_file};
+use crate::config::{copy_file, get_app_config_dir, get_app_config_path, write_json_file};
 use crate::provider::ProviderManager;
 
 /// 应用类型
@@ -78,6 +78,23 @@ impl MultiAppConfig {
 
             let config = Self { version: 2, apps };
 
+            // 迁移前备份旧版(v1)配置文件
+            let backup_dir = get_app_config_dir();
+            let ts = std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .unwrap_or_default()
+                .as_secs();
+            let backup_path = backup_dir.join(format!("config.v1.backup.{}.json", ts));
+
+            match copy_file(&config_path, &backup_path) {
+                Ok(()) => log::info!(
+                    "已备份旧版配置文件: {} -> {}",
+                    config_path.display(),
+                    backup_path.display()
+                ),
+                Err(e) => log::warn!("备份旧版配置文件失败: {}", e),
+            }
+
             // 保存迁移后的配置
             config.save()?;
             return Ok(config);

src/lib/tauri-api.ts

@@ -167,6 +167,8 @@ export const tauriAPI = {
     }
   },
 
+  // （保留空位，取消迁移提示）
+
   // 选择配置文件（Tauri 暂不实现，保留接口兼容性）
   selectConfigFile: async (): Promise<string | null> => {
     console.warn("selectConfigFile 在 Tauri 版本中暂不支持");