Add user account settings page with profile management

- Add /account route with profile form (firstName, lastName, address, IBAN)
- Create UserProfile type and MongoDB users collection
- Implement server actions for getting and updating user profile
- Add Account Circle icon to PageHeader linking to /account
- Install Material UI icons for account icon
- Add form input disabling during save with loading spinner
- Add cancel button to discard changes and return home
- Add English and Croatian translations for account page
- Update locale names with flag emojis in language selector

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/i18n.ts

@@ -6,8 +6,8 @@ import { Formats, TranslationValues } from 'next-intl';
 export const locales = ['en', 'hr'];
 
 export const localeNames:Record<string,string> = {
-  en: 'English',
-  hr: 'Hrvatski'
+  en: '🇬🇧 En',
+  hr: '🇭🇷 Hr'
 };
 
 export const defaultLocale = 'hr';