Add username validation for Ko-fi

[kaifcodec]

• Add username validation for Ko-fi in a new category donation/.
• Update __main__.py and core/orchestrator.py to recognize the new category.
• Ensure the new module follows the same structure and conventions as other social/creator modules.

[VamatoHD]

@kaifcodec After some brief testing, I found out Ko-fi aggressively blocks non-browser requests. The only solution is to use a library like Playwright to mimic a browser and check if the user exists. Since this library is kind of heavy, it would need to be optional, and implementing it is hard (the part of just opening one browser for every site that requires it) but doable.

[kaifcodec]

@VamatoHD If ko-fi blocks the non-browser requests then I think it would better not to implement it in our list, atleast not now.

You are correct that selenium or playwright like headless browsers are way too heavy to use just for simple username checks.