fix: decode values of useParams and fix redirection in CheckSlug

Closes #1720 (closed)

It's similar to this issue !1198 (6ac7922a)

but I addressed it differently by applying the decode function on a higher level because this issue can be faced in many places.

For the CheckSlug component, I was getting another error [1] when I try to visit a page with a wrong slug. surrounding the redirect with a useEffect, fixed the issue!

[1]