♻️(frontend) extract hardcoded domain to use dynamic window origin

Replace hardcoded visio.numerique.gouv.fr with automatic detection based on
window.location.origin for better environment flexibility.

src/frontend/src/components/NotFoundScreen.tsx

@@ -10,8 +10,7 @@ export const NotFoundScreen = () => {
     <Screen layout="centered">
       <CenteredContent title={t('notFound.heading')} withBackButton>
         <Text centered>
-          {t('notFound.body')}{' '}
-          <Bold>https://visio.numerique.gouv.fr/xxx-yyyy-zzz.</Bold>
+          {t('notFound.body')} <Bold>{window.origin}/xxx-yyyy-zzz.</Bold>
         </Text>
       </CenteredContent>
     </Screen>

src/frontend/src/features/home/components/JoinMeetingDialog.tsx

@@ -23,7 +23,7 @@ export const JoinMeetingDialog = () => {
           name="roomId"
           label={t('joinInputLabel')}
           description={t('joinInputExample', {
-            example: 'https://visio.numerique.gouv.fr/azer-tyu-qsdf',
+            example: window.origin + '/azer-tyu-qsdf',
           })}
           validate={(value) => {
             return !isRoomValid(value.trim()) ? (