Add Apple Sign In welcome email, notification preferences on registration, and contractor sharing tests

- Send welcome email to new users who sign up via Apple Sign In
- Create notification preferences (all enabled) when new accounts are created
- Add comprehensive integration tests for contractor sharing:
  - Personal contractors only visible to creator
  - Residence-tied contractors visible to all users with residence access
  - Update/delete access control for shared contractors

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

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

internal/services/auth_service.go

@@ -33,8 +33,9 @@ var (
 
 // AuthService handles authentication business logic
 type AuthService struct {
-	userRepo *repositories.UserRepository
-	cfg      *config.Config
+	userRepo         *repositories.UserRepository
+	notificationRepo *repositories.NotificationRepository
+	cfg              *config.Config
 }
 
 // NewAuthService creates a new auth service
@@ -45,6 +46,11 @@ func NewAuthService(userRepo *repositories.UserRepository, cfg *config.Config) *
 	}
 }
 
+// SetNotificationRepository sets the notification repository for creating notification preferences
+func (s *AuthService) SetNotificationRepository(notificationRepo *repositories.NotificationRepository) {
+	s.notificationRepo = notificationRepo
+}
+
 // Login authenticates a user and returns a token
 func (s *AuthService) Login(req *requests.LoginRequest) (*responses.LoginResponse, error) {
 	// Find user by username or email
@@ -134,6 +140,14 @@ func (s *AuthService) Register(req *requests.RegisterRequest) (*responses.Regist
 		fmt.Printf("Failed to create user profile: %v\n", err)
 	}
 
+	// Create notification preferences with all options enabled
+	if s.notificationRepo != nil {
+		if _, err := s.notificationRepo.GetOrCreatePreferences(user.ID); err != nil {
+			// Log error but don't fail registration
+			fmt.Printf("Failed to create notification preferences: %v\n", err)
+		}
+	}
+
 	// Create auth token
 	token, err := s.userRepo.GetOrCreateToken(user.ID)
 	if err != nil {
@@ -523,6 +537,14 @@ func (s *AuthService) AppleSignIn(ctx context.Context, appleAuth *AppleAuthServi
 		_ = s.userRepo.SetProfileVerified(user.ID, true)
 	}
 
+	// Create notification preferences with all options enabled
+	if s.notificationRepo != nil {
+		if _, err := s.notificationRepo.GetOrCreatePreferences(user.ID); err != nil {
+			// Log error but don't fail registration
+			fmt.Printf("Failed to create notification preferences: %v\n", err)
+		}
+	}
+
 	// Link Apple ID
 	appleAuthRecord := &models.AppleSocialAuth{
 		UserID:         user.ID,