[e.cash] Fix spline render

Summary:
Noticed a bunch of spline 3d errors in the console that were coming from the two instances of spline (mobile and desktop)

The css only conditional rendering apparently was not enough, so the mobile spline was still trying to load on desktop and vice versa, causing some WebGL console erros that you can see in master branch

Adding a media query hook to check the screen size and conditionally render the correct spline scene

Test Plan: Preview and check. Hero section should look the same, but no WebGL console erros compared to master

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D18533