feat: add PlanningDurationService for estimating planning duration

- Implemented PlanningDurationService to provide an indicative wait time before calculation based on user input and calendar settings.
- Introduced duration estimation logic that considers horizon dates, balances, and rules without triggering a calculation.
- Enhanced user input component to display estimated duration using the new service.
- Updated translation files to include new duration estimate strings in multiple languages.
- Added tests for PlanningDurationService to ensure accurate duration estimation and calibration.
- Refactored leave planner service to remove hardcoded deadlines and improve worker responsiveness.

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

@@ -25,6 +25,9 @@
 
 	<app-rules-panel></app-rules-panel>
 
+	@if (duration.estimate()) {
+		<p id="planning-duration-estimate" class="duration-estimate">{{ durationLabel() }}</p>
+	}
 	<button
 		mat-flat-button
 		class="calculate-button"
@@ -32,7 +35,9 @@
 		type="button"
 		[disabled]="!!calendarSettings.planningHorizonError()"
 		[attr.aria-describedby]="
-			calendarSettings.planningHorizonError() ? 'invalid-planning-horizon' : null
+			calendarSettings.planningHorizonError()
+				? 'invalid-planning-horizon'
+				: 'planning-duration-estimate'
 		"
 		(click)="triggerComputation()"
 	>