refactor: migrate testing framework from Karma/Jasmine to Vitest with Angular support

src/app/services/calendar-service.spec.ts

@@ -1,4 +1,5 @@
 import { TestBed } from '@angular/core/testing';
+import { vi } from 'vitest';
 import { provideZonelessChangeDetection } from '@angular/core';
 import {
 	CalendarService,
@@ -228,20 +229,20 @@ describe('SelectedDates', () => {
 				{ id: '3', type: RuleType.IF_THEN, enabled: true } as IfThenRule,
 			];
 
-			const applyTimeWindowRulesSpy = spyOn(selectedDates, 'applyTimeWindowRules');
-			const applyIfThenRulesSpy = spyOn(selectedDates, 'applyIfThenRules');
+			const applyTimeWindowRulesSpy = vi.spyOn(selectedDates, 'applyTimeWindowRules');
+			const applyIfThenRulesSpy = vi.spyOn(selectedDates, 'applyIfThenRules');
 
 			await selectedDates.optimizeVacations(vacationDays, rules, calendarService);
 
-			expect(applyIfThenRulesSpy.calls.count()).toBe(2);
-			expect(applyTimeWindowRulesSpy.calls.count()).toBe(1);
+			expect(applyIfThenRulesSpy.mock.calls.length).toBe(2);
+			expect(applyTimeWindowRulesSpy.mock.calls.length).toBe(1);
 
 			// First rule is IF_THEN
-			expect(applyIfThenRulesSpy.calls.argsFor(0)[1][0].id).toBe('1');
+			expect(applyIfThenRulesSpy.mock.calls[0][1][0].id).toBe('1');
 			// Second rule is TIME_WINDOW
-			expect(applyTimeWindowRulesSpy.calls.argsFor(0)[1][0].id).toBe('2');
+			expect(applyTimeWindowRulesSpy.mock.calls[0][1][0].id).toBe('2');
 			// Third rule is IF_THEN
-			expect(applyIfThenRulesSpy.calls.argsFor(1)[1][0].id).toBe('3');
+			expect(applyIfThenRulesSpy.mock.calls[1][1][0].id).toBe('3');
 		});
 
 		it('should apply time window rules', () => {
@@ -268,7 +269,7 @@ describe('SelectedDates', () => {
 			];
 
 			// Mock monthsInAYearFromNow to return a controlled range of days
-			spyOn(calendarService, 'monthsInAYearFromNow').and.returnValue([
+			vi.spyOn(calendarService, 'monthsInAYearFromNow').mockReturnValue([
 				[
 					[
 						new Date(futureYear, 11, 20),
@@ -376,7 +377,7 @@ describe('SelectedDates', () => {
 				},
 			];
 
-			spyOn(calendarService, 'monthsInAYearFromNow').and.returnValue([
+			vi.spyOn(calendarService, 'monthsInAYearFromNow').mockReturnValue([
 				[
 					[
 						new Date(futureYear, 6, 1),