CSV import character encoding is automatically verified

The system will automatically verify that all CSV files are in the correct UTF-8 character encoding before import. If the file is not in UTF-8 format and contains special characters or diacritics, the import will be halted, and the user will be shown a clear error message. This prevents common issues where diacritics might corrupt database entries or cause incorrect product information. The user will be instructed to save the file again with UTF-8 encoding and try again. This improvement ensures data integrity and facilitates error tracking, particularly during import.