Refactor: Overhaul Monolithic Architecture into Modular Frontend Stack

[Amir-Mohammd-Asadjoo]

Description:
"Hi there! I took a deep dive into the project and completely refactored the repository. Initially, the entire application (HTML, CSS, JS, filtering logic, and state) was tightly coupled into a single monolithic index.html file, which makes it hard to maintain or scale.

I have broken down the codebase into a professional, clean Modular Frontend Architecture:

1. Stripped index.html down to a clean markup skeleton.
2. Separated logic into independent ES6 modules (state, filter, search, sort, render).
3. Added professional client-side export utilities (Excel and PDF).
4. Structured the CSS using custom properties/variables for global Dark/Light mode support and dynamic UI components (modals/toasts).

This makes the project completely clean, production-ready, and super easy for others to contribu