Force Uppercase to Lowercase Conversion (.CSV → .csv)

Description:
Some files are generated or uploaded with uppercase extensions (e.g., .CSV), causing Legale to reject them.
The system must automatically convert any uppercase or mixed-case extensions to lowercase (.CSV → .csv) in all scenarios — including file generation, upload, and validation.

Proposed Solution:

1. Detect files with .CSV or mixed-case extensions (e.g., .Csv, .CsV).

2. Automatically rename the file extension to .csv before saving or processing.

3. Keep the current validation logic unchanged.

Objective:
Ensure consistent file handling and prevent errors caused by case-sensitive extensions.