Refactor OAuth divider component and update README visuals

- Simplified the OAuth divider component with a cleaner layout for improved UI consistency.
- Updated README to include and organize new visuals for key sections, enhancing documentation clarity.

frontend/src/components/auth/OAuthButtons.tsx

@@ -144,13 +144,10 @@ function Divider() {
   const t = useTranslations('auth.oauth');
 
   return (
-    <div className="relative">
-      <div className="absolute inset-0 flex items-center">
-        <span className="w-full border-t" />
-      </div>
-      <div className="relative flex justify-center text-xs uppercase">
-        <span className="bg-background px-2 text-muted-foreground">{t('divider')}</span>
-      </div>
+    <div className="flex items-center gap-4">
+      <span className="h-px flex-1 bg-border" />
+      <span className="text-xs uppercase text-muted-foreground">{t('divider')}</span>
+      <span className="h-px flex-1 bg-border" />
     </div>
   );
 }