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/services/leave-planner.worker.ts

@@ -63,6 +63,7 @@ type WorkerRequest =
 	  };
 
 type WorkerResponse =
+	| { type: 'heartbeat' }
 	| { type: 'progress'; stage: string }
 	| { type: 'trace-overhead'; totalMs: number }
 	| { type: 'checkpoint'; plan: PlanOutcome; state?: PlanningTraceState }
@@ -301,7 +302,12 @@ worker.onmessage = async (event: MessageEvent<WorkerRequest>) => {
 				calculationComplete: false,
 			};
 			activeTraceDelivery = traceDelivery;
+			// The cooperative driver yields during preparation and search, even within one phase.
+			const heartbeat = () =>
+				worker.postMessage({ type: 'heartbeat' } satisfies WorkerResponse);
+			const heartbeatTimer = setInterval(heartbeat, 1000);
 			try {
+				heartbeat();
 				outcome = await calculatePlanningAsyncInternal(
 					{
 						...event.data.request,
@@ -351,6 +357,7 @@ worker.onmessage = async (event: MessageEvent<WorkerRequest>) => {
 				} satisfies WorkerResponse);
 				return;
 			} finally {
+				clearInterval(heartbeatTimer);
 				if (activeCalculation === calculation) activeCalculation = undefined;
 			}
 			if (!outcomePosted)