Update error and not-found page styles

Removed unused import from error page and adjusted the heading styles on both the 500 error page and the 404 not-found page. By increasing the size of the text headings and updating the font to 'font-heading', the pages are now more consistent with the overall design layout.

apps/web/app/not-found.tsx

@@ -38,7 +38,7 @@ const NotFoundPage = async () => {
       >
         <div className={'flex flex-col items-center space-y-12'}>
           <div>
-            <h1 className={'text-8xl font-extrabold'}>404 :(</h1>
+            <h1 className={'font-heading text-9xl font-extrabold'}>404 :(</h1>
           </div>
 
           <div className={'flex flex-col items-center space-y-4'}>