feat: implement email-optional authentication

- Make email field optional in database schema
- Update user creation to handle null emails
- Enhance notification service to gracefully skip email for users without email addresses
- Add validation in email service for null/empty emails
- Create comprehensive documentation for Clerk configuration
- Add test script for email-optional functionality
- Update all user creation points (userService, eventController, reportController)

Users can now sign up with just username and password. Email notifications
are gracefully skipped for users without email addresses, while in-app
notifications continue to work for all users.

Closes: Email-optional authentication requirement

src/components/auth/index.ts.backup.ts

@@ -0,0 +1,6 @@
+export { ProtectedRoute } from './ProtectedRoute';
+export { UserProfile } from './UserProfile';
+export { SignInPage } from './SignInPage';
+export { SignUpPage } from './SignUpPage';
+export { NotificationSettings } from './NotificationSettings';
+export type { NotificationPreferences, AreaOfInterest } from './NotificationSettings';