[Bug] scrollBtn null dereference across multiple HTML files

[saurabhhhcodes]

login.html, register.html, quiz.html, admin.html: getElementById scrollToTop runs before element exists

[malvikakamble13-bit]

Hi! I am a GSSoC '26 contributor and I would love to solve this issue by adding the missing scrollToTop button to the specified HTML files. Could you please assign this issue to me?

[toshigoel10]

/assign