refactor(planning): give planning calculations one state owner

PlanningCalculationService now builds the submitted request, owns the
pending and accepted calculation state, and delivers explanations for
the accepted calculation only. The duration estimator reads the same
request. The calendar and leave-balance summary consume the accepted
outcome instead of coordinating writable state on the input service.

Refs #275

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/services/user-input-service.spec.ts

@@ -46,7 +46,6 @@ describe('UserInputService', () => {
 			{ date: '2024-01-02', type: 'other' },
 		]);
 		expect(service.vacationNumberSignal()).toBe(balances);
-		expect(service.computeTriggerSignal()).toBe(0);
 		expect(localStorage.getItem('leaveBalances')).toBeNull();
 	});
 
@@ -119,7 +118,6 @@ describe('UserInputService', () => {
 		]);
 		expect(save).toHaveBeenCalledTimes(3);
 		expect(service.vacationNumberSignal()).toBe(balances);
-		expect(service.computeTriggerSignal()).toBe(0);
 	});
 
 	it('restores an empty list when saved declarations are unreadable', () => {