Modernize CI/CD pipeline with comprehensive automation (#25)

* Initial plan

* Add comprehensive CI/CD workflows and tooling

- Add PR validation workflow with lint, format, type check, test, and build steps
- Improve Docker build workflow with caching, security scanning, and manual trigger
- Add CodeQL security analysis workflow
- Add Dependabot configuration for automated dependency updates
- Configure ESLint with TypeScript support
- Add npm scripts for linting and formatting
- Format code with Prettier
- Fix linting issues in source code

Co-authored-by: THoguet <61246905+THoguet@users.noreply.github.com>

* Update README and fix build configuration

- Add CI/CD documentation to README
- Document code quality tools and scripts
- Disable font optimization in production build to avoid network dependency
- Add build cache configuration for GitHub Actions

Co-authored-by: THoguet <61246905+THoguet@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: THoguet <61246905+THoguet@users.noreply.github.com>

src/app/services/calendar-service.ts

@@ -28,8 +28,8 @@ export class CalendarService {
 
 	// Get selected dates from current date to the next year
 	getSelectedDatesFromNow(): SelectedDates {
-		const holidays = this.getHolidays();
-		let selectedDates: SelectedDates = new SelectedDates();
+		const _holidays = this.getHolidays();
+		const selectedDates: SelectedDates = new SelectedDates();
 		// Logic to populate selectedDates from now until the next year
 		return selectedDates;
 	}
@@ -37,7 +37,7 @@ export class CalendarService {
 	getSelectedDatesForYear(): SelectedDates {
 		const holidays = this.getHolidays();
 		const monthInAYear = this.monthsInAYearFromNow();
-		let selectedDates: SelectedDates = new SelectedDates();
+		const selectedDates: SelectedDates = new SelectedDates();
 
 		// Use DateCacheService to get today's date components
 		const {
@@ -519,7 +519,7 @@ export class SelectedDates implements SelectedDateInterface {
 			const daysInRange = selectedDate.getLengthInDays();
 
 			// For each day in the range, add it to the appropriate month
-			let currentDate = new Date(selectedDate.range.start);
+			const currentDate = new Date(selectedDate.range.start);
 			for (let i = 0; i < daysInRange; i++) {
 				const monthKey = currentDate.getFullYear() * 12 + currentDate.getMonth();
 				monthCounts.set(monthKey, (monthCounts.get(monthKey) ?? 0) + 1);
@@ -719,7 +719,10 @@ export class SelectedDates implements SelectedDateInterface {
 		}
 	}
 
-	lookForVacation(vacType: DayType, calendarService: CalendarService): { apply: () => void; heuristic: number } {
+	lookForVacation(
+		vacType: DayType,
+		calendarService: CalendarService,
+	): { apply: () => void; heuristic: number } {
 		const daysOfYear = calendarService.monthsInAYearFromNow();
 		const now = new Date();
 		now.setHours(0, 0, 0, 0);