refactor(database): 移除不必要的state_guard释放操作

移除db_switch_connection函数中多余的drop(state_guard)调用，因为Rust的RAII机制会自动处理资源释放

src-tauri/src/commands/database.rs

@@ -1169,7 +1169,6 @@ pub async fn db_switch_connection(
             conn,
         )
     };
-    drop(state_guard);
 
     {
         let settings_db_path = sqlite_db_path(&app_handle)?;