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-settings/user-settings.ts

@@ -9,6 +9,7 @@ import {
 import { MatFormFieldModule } from '@angular/material/form-field';
 import { MatSelectModule } from '@angular/material/select';
 import { MatSlideToggle } from '@angular/material/slide-toggle';
+import { MatInputModule } from '@angular/material/input';
 import { CalendarSettingsService } from '../../services/calendar-settings-service';
 import { ThemeService } from '../../services/theme-service';
 import { TranslationService } from '../../services/translation-service';
@@ -24,6 +25,7 @@ import { TranslationService } from '../../services/translation-service';
 		MatFormFieldModule,
 		MatSelectModule,
 		MatSlideToggle,
+		MatInputModule,
 	],
 	templateUrl: './user-settings.html',
 	styleUrl: './user-settings.scss',
@@ -32,7 +34,8 @@ import { TranslationService } from '../../services/translation-service';
 export class UserSettings {
 	protected readonly themeService = inject(ThemeService);
 	protected readonly translationService = inject(TranslationService);
-	protected readonly showWeekNumbers = inject(CalendarSettingsService).get('showWeekNumbers');
+	protected readonly calendarSettings = inject(CalendarSettingsService);
+	protected readonly showWeekNumbers = this.calendarSettings.get('showWeekNumbers');
 	protected readonly tr = this.translationService.tr;
 	protected readonly themePreferences = ['system', 'light', 'dark'] as const;
 }