Bugfix/V2/pdfa_extension (#4336)

Changes fallback pdfa extension pdf when a filename isnt returned for
convert.
Also fixes ui bug with footer and pop ups

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Co-authored-by: Connor Yoh <connor@stirlingpdf.com>

frontend/src/components/shared/Footer.tsx

@@ -24,7 +24,6 @@ export default function Footer({
   return (
     <div style={{
       height: 'var(--footer-height)',
-      zIndex: 999999,
       backgroundColor: 'var(--mantine-color-gray-1)',
       borderTop: '1px solid var(--mantine-color-gray-2)',
       display: 'flex',