refactor: unify date handling with utility functions

- Replaced direct date manipulations with utility functions like `getToday`, `parseDate`, and `createDateFromParts` across various components and services for consistency.
- Updated date initialization in `JiraAnalyticsService`, `BackupService`, and `DailyClient` to improve clarity and maintainability.
- Enhanced date parsing in forms and API routes to ensure proper handling of date strings.

src/app/api/daily/route.ts

@@ -1,6 +1,6 @@
 import { NextResponse } from 'next/server';
 import { dailyService } from '@/services/daily';
-import { getToday, parseDate, isValidAPIDate } from '@/lib/date-utils';
+import { getToday, parseDate, isValidAPIDate, createDateFromParts } from '@/lib/date-utils';
 
 /**
  * API route pour récupérer la vue daily (hier + aujourd'hui)
@@ -79,9 +79,9 @@ export async function POST(request: Request) {
     if (typeof body.date === 'string') {
       // Si c'est une string YYYY-MM-DD, créer une date locale
       const [year, month, day] = body.date.split('-').map(Number);
-      date = new Date(year, month - 1, day); // month est 0-indexé
+      date = createDateFromParts(year, month, day);
     } else {
-      date = new Date(body.date);
+      date = parseDate(body.date);
     }
     
     if (isNaN(date.getTime())) {