fix(assigned-site-dialog): hide Lønregler section when no pay rule sets exist

Gate both the section header and the PayRuleSet dropdown on
availablePayRuleSets.length > 0 so the entire Lønregler block is hidden
when no pay rule sets have been configured in the system.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: renemadsen

eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.html

@@ -30,10 +30,10 @@
         </mat-checkbox>
       </div>
 
-      <!-- ========= Payroll rules ========= -->
-      <h3 class="section-header" *ngIf="!data.resigned && selectCurrentUserIsAdmin$ | async">{{ 'Payroll rules' | translate }}</h3>
+      <!-- ========= Payroll rules (hidden when no pay rule sets exist) ========= -->
+      <h3 class="section-header" *ngIf="!data.resigned && availablePayRuleSets.length > 0 && selectCurrentUserIsAdmin$ | async">{{ 'Payroll rules' | translate }}</h3>
 
-      <div class="d-flex flex-row" *ngIf="!data.resigned && selectCurrentUserIsAdmin$ | async">
+      <div class="d-flex flex-row" *ngIf="!data.resigned && availablePayRuleSets.length > 0 && selectCurrentUserIsAdmin$ | async">
         <mat-form-field class="p-1 w-100">
           <mat-label>{{ 'Pay Rule Set' | translate }}</mat-label>
           <mtx-select