Namespace collisions

Move the classes `db_search.php`, `file_search.php`, `files.php`, `files_table.php`, `helper.php`, `replace_error_handler.php`, `search.php`, `search_table.php` to the `local/` folder to avoid namespace collisions.  

![Image](https://github.com/user-attachments/assets/c1b3179b-cc3f-4b37-b825-e76fcf085913)