Add email notification preference for task completion

- Add EmailTaskCompleted field to NotificationPreference model
- Update notification repository to include email preference in queries
- Check email preference before sending task completion emails
- Add email preference toggle to admin panel notification-prefs page
- Update API types for email preference support

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

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

internal/services/notification_service.go

@@ -190,6 +190,9 @@ func (s *NotificationService) UpdatePreferences(userID uint, req *UpdatePreferen
 	if req.WarrantyExpiring != nil {
 		prefs.WarrantyExpiring = *req.WarrantyExpiring
 	}
+	if req.EmailTaskCompleted != nil {
+		prefs.EmailTaskCompleted = *req.EmailTaskCompleted
+	}
 
 	if err := s.notificationRepo.UpdatePreferences(prefs); err != nil {
 		return nil, err
@@ -358,17 +361,21 @@ type NotificationPreferencesResponse struct {
 	TaskAssigned     bool `json:"task_assigned"`
 	ResidenceShared  bool `json:"residence_shared"`
 	WarrantyExpiring bool `json:"warranty_expiring"`
+
+	// Email preferences
+	EmailTaskCompleted bool `json:"email_task_completed"`
 }
 
 // NewNotificationPreferencesResponse creates a NotificationPreferencesResponse
 func NewNotificationPreferencesResponse(p *models.NotificationPreference) *NotificationPreferencesResponse {
 	return &NotificationPreferencesResponse{
-		TaskDueSoon:      p.TaskDueSoon,
-		TaskOverdue:      p.TaskOverdue,
-		TaskCompleted:    p.TaskCompleted,
-		TaskAssigned:     p.TaskAssigned,
-		ResidenceShared:  p.ResidenceShared,
-		WarrantyExpiring: p.WarrantyExpiring,
+		TaskDueSoon:        p.TaskDueSoon,
+		TaskOverdue:        p.TaskOverdue,
+		TaskCompleted:      p.TaskCompleted,
+		TaskAssigned:       p.TaskAssigned,
+		ResidenceShared:    p.ResidenceShared,
+		WarrantyExpiring:   p.WarrantyExpiring,
+		EmailTaskCompleted: p.EmailTaskCompleted,
 	}
 }
 
@@ -380,6 +387,9 @@ type UpdatePreferencesRequest struct {
 	TaskAssigned     *bool `json:"task_assigned"`
 	ResidenceShared  *bool `json:"residence_shared"`
 	WarrantyExpiring *bool `json:"warranty_expiring"`
+
+	// Email preferences
+	EmailTaskCompleted *bool `json:"email_task_completed"`
 }
 
 // DeviceResponse represents a device in API response