Fixed file extension extraction issue for filenames with multiple dots.

[NimeshaKahingala]

Refactored File Extension Extraction

• Improved file extension extraction to handle filenames with multiple dots dynamically.
• Instead of checking for fixed extensions (.yml or .json) and slicing based on fixed lengths, the new solution uses lastIndexOf('.') to reliably separate the filename and extension.
• This improves flexibility by supporting any file extension while preventing incorrect slicing for filenames with multiple dots.

Backend Refactor

• Moved the file extension splitting logic to the backend to keep the frontend logic cleaner and abstract internal implementation details.