fix(01-02): resolve compilation errors in auth models

- Fixed import path in AuthRepository to reach core errors
- Updated AuthUser.fromSupabase() to handle DateTime parsing safely
- Added UnknownAuthException for fallback error handling
- Fixed null-aware operators in AuthUser model
- All authentication files now compile without errors

lib/core/errors/auth_exceptions.dart

@@ -146,6 +146,19 @@ class AuthDisabledException extends AuthException {
         );
 }
 
+/// Exception thrown for unknown authentication errors
+class UnknownAuthException extends AuthException {
+  const UnknownAuthException({
+    String message = 'An unknown authentication error occurred',
+    String? code,
+    dynamic originalError,
+  }) : super(
+          message: message,
+          code: code ?? 'UNKNOWN_ERROR',
+          originalError: originalError,
+        );
+}
+
 /// Utility class for converting Supabase errors to custom exceptions
 /// 
 /// Provides a centralized way to map Supabase error responses
@@ -263,7 +276,7 @@ class AuthExceptionFactory {
     }
     
     // Fallback for unknown errors
-    return AuthException(
+    return UnknownAuthException(
       message: _extractUserFriendlyMessage(errorMessage) ?? 'Authentication failed',
       code: errorCode,
       originalError: error,

lib/features/authentication/data/models/auth_user.dart

@@ -45,11 +45,11 @@ class AuthUser {
     return AuthUser(
       id: user.id,
       email: user.email ?? '',
-      createdAt: user.createdAt ?? DateTime.now(),
+      createdAt: DateTime.tryParse(user.createdAt.toString()) ?? DateTime.now(),
       emailVerified: user.emailConfirmedAt != null,
       displayName: user.userMetadata?['display_name'] as String?,
       avatarUrl: user.userMetadata?['avatar_url'] as String?,
-      lastSignInAt: user.lastSignInAt,
+      lastSignInAt: DateTime.tryParse(user.lastSignInAt.toString()),
     );
   }
   

lib/features/authentication/domain/repositories/auth_repository.dart

@@ -1,5 +1,5 @@
 import '../../data/models/auth_user.dart';
-import '../../../core/errors/auth_exceptions.dart';
+import '../../../../core/errors/auth_exceptions.dart';
 
 /// Authentication repository interface defining all authentication operations.
 ///