feat(planner): implement cancellation for planning calculations

- Refactor leave-planner.worker.ts to support cancellation of ongoing calculations.
- Introduce `calculatePlanningAsyncInternal` for asynchronous planning calculations.
- Add cancellation handling in the worker message event.
- Update planning-date.ts with new utility functions for date manipulation.
- Extend translation-service.ts and translation files (en.json, de.json, es.json, fr.json) to include new strings related to planning horizon and cancellation.
- Create documentation for the cancellation feature in planner-cancellation.md.
- Add unit tests for cancellation functionality in leave-planner-cancellation.spec.ts and leave-planner.worker.spec.ts.

#57 #58

src/app/components/user-input/user-input.ts

@@ -8,6 +8,7 @@ import { DayInput } from '../userInput/day-input/day-input';
 import { MatButtonModule } from '@angular/material/button';
 import { VacDay } from '../../services/calendar-service';
 import { TranslationService } from '../../services/translation-service';
+import { CalendarSettingsService } from '../../services/calendar-settings-service';
 
 @Component({
 	selector: 'app-user-input',
@@ -26,6 +27,7 @@ import { TranslationService } from '../../services/translation-service';
 })
 export class UserInput {
 	private userInputService: UserInputService = inject(UserInputService);
+	protected readonly calendarSettings = inject(CalendarSettingsService);
 	protected readonly translationService = inject(TranslationService);
 
 	get tr() {
@@ -99,6 +101,7 @@ export class UserInput {
 	}
 
 	public triggerComputation() {
+		if (this.calendarSettings.planningHorizonError()) return;
 		this.userInputService.requestComputation();
 	}
 }