docs(cleanup): remove 'current' as special provider; align UI/messages and migration naming to 'default' and one-time import rule

- App: update auto-import message to '默认供应商'
- README: clarify default import only when providers are empty
- Plan doc: replace 'current entry' wording with current pointer (manager.current)
- Migration: name live-imported item 'default' instead of 'current'

src-tauri/src/migration.rs

@@ -164,7 +164,7 @@ pub fn migrate_copies_into_config(config: &mut MultiAppConfig) -> Result<bool, S
         let settings_path = crate::config::get_claude_settings_path();
         if settings_path.exists() {
             match crate::config::read_json_file::<Value>(&settings_path) {
-                Ok(val) => Some(("current".to_string(), val)),
+                Ok(val) => Some(("default".to_string(), val)),
                 Err(e) => {
                     log::warn!("读取 Claude live 配置失败: {}", e);
                     None
@@ -269,7 +269,7 @@ pub fn migrate_copies_into_config(config: &mut MultiAppConfig) -> Result<bool, S
                     } else {
                         String::new()
                     };
-                    Some(("current".to_string(), serde_json::json!({"auth": auth, "config": cfg})))
+                    Some(("default".to_string(), serde_json::json!({"auth": auth, "config": cfg})))
                 }
                 Err(e) => {
                     log::warn!("读取 Codex live auth.json 失败: {}", e);
@@ -350,7 +350,7 @@ pub fn migrate_copies_into_config(config: &mut MultiAppConfig) -> Result<bool, S
         }
     }
 
-    // 若 current 为空，将 live 导入项设为 current
+    // 若当前为空，将 live 导入项设为当前
     {
         let manager = config.get_manager_mut(&AppType::Claude).unwrap();
         if manager.current.is_empty() {