✨(frontend) add h1 for SR on 40X pages and remove alt texts

improves screen reader support on error pages by clarifying structure

Signed-off-by: Cyril <c.gromoff@gmail.com>

src/frontend/apps/impress/src/pages/401.tsx

@@ -39,10 +39,13 @@ const Page: NextPageWithLayout = () => {
         $gap="1rem"
         $padding={{ bottom: '2rem' }}
       >
+        <Text as="h1" $textAlign="center" className="sr-only">
+          {t('401 Unauthorized')} - {t('Docs')}
+        </Text>
         <Image
           className="c__image-system-filter"
           src={img401}
-          alt={t('Image 401')}
+          alt=""
           style={{
             maxWidth: '100%',
             height: 'auto',

src/frontend/apps/impress/src/pages/404.tsx

@@ -35,10 +35,13 @@ const Page: NextPageWithLayout = () => {
         $gap="1rem"
         $padding={{ bottom: '2rem' }}
       >
+        <Text as="h1" $textAlign="center" className="sr-only">
+          {t('Page Not Found - Error 404')} - {t('Docs')}
+        </Text>
         <Image
           className="c__image-system-filter"
           src={img403}
-          alt={t('Image 403')}
+          alt=""
           style={{
             maxWidth: '100%',
             height: 'auto',