Refactor server.R code

[AlexGherardelli]

Currently the server side of this Rshiny application suffers from scode issues. The current implementation lacks separation of concerns and mixes multiple responsibilities including:

• Data import
• Indicator computation
• Data processing
• Data validation

The goal is to modularize the codebase for maintainability, scalability, and testability.

Current issues

No separation of concerns: All logic is embedded in a single file, making it hard to debug or extend.
Poor readability: Lack of comments and structure makes onboarding new developers difficult.
Tight coupling: UI and server logic are intertwined with data processing and validation.
No testing: No unit tests or validation mechanisms for core computations.

[paololucchino]

I can help out here (assigning myself) but I imagine this will be a group effort! =)