They are kept separate because the fiqh treats them differently, and because commingling them cannot be undone afterwards.
Zakāh الزكاة
Will fund people, not the platform: scholarships and device or connectivity support for students in need, and stipends for teachers who are themselves zakāh-eligible.
It will never pay for servers, software or administration. Any proposal to change that requires written board review first.
Sadaqah الصدقة
General giving. Funds everything zakāh may not: hosting, the site itself, editorial work, translation, and the cost of keeping all of it free.
Every donation will be tagged at the point of collection — zakāh or not, restricted or not — because that cannot be reconstructed later.
Sadaqah jāriya صدقة جارية
Recurring monthly giving, and in time a restricted endowment whose principal is preserved and whose income keeps the lessons online after the founders are gone.
Where a donor intends the principal to be permanently inviolable, that will be written into the gift instrument itself, not assumed.