fix: resolve date formatting error in event creation

- Fix TypeError "e.match is not a function" when creating events
- Update useLocalizedDate hook to handle both string and object date formats
- Add type safety for date format configuration
- Fix date format strings to use correct date-fns format (lowercase)
- Ensure backward compatibility with existing date settings

The issue was caused by SettingsPage saving date formats as objects
while useLocalizedDate expected strings. This fix handles both formats
gracefully and prevents the error page redirect.

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

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

frontend/src/services/publicSettings.service.ts

@@ -15,7 +15,7 @@ export interface PublicSettings {
   theme_config: any;
   default_language: string;
   enable_analytics: boolean;
-  general_date_format: string;
+  general_date_format: string | { format: string; locale: string };
   enable_recaptcha: boolean;
   recaptcha_site_key: string | null;
   maintenance_mode: boolean;