fix(store): SetHostAlwaysOn returns ErrNotFound; test agent-token lookup path

internal/store/hosts.go

@@ -388,11 +388,14 @@ func (s *Store) SetHostAlwaysOn(ctx context.Context, hostID string, alwaysOn boo
 	if alwaysOn {
 		v = 1
 	}
-	_, err := s.db.ExecContext(ctx,
+	res, err := s.db.ExecContext(ctx,
 		`UPDATE hosts SET always_on = ? WHERE id = ?`, v, hostID)
 	if err != nil {
 		return fmt.Errorf("store: set host always_on: %w", err)
 	}
+	if n, _ := res.RowsAffected(); n == 0 {
+		return ErrNotFound
+	}
 	return nil
 }