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/lib/jira-period-filter.ts

@@ -1,4 +1,5 @@
 import { JiraAnalytics } from './types';
+import { getToday, subtractDays, parseDate } from './date-utils';
 
 export type PeriodFilter = '7d' | '30d' | '3m' | 'current';
 
@@ -9,18 +10,18 @@ export function filterAnalyticsByPeriod(
   analytics: JiraAnalytics, 
   period: PeriodFilter
 ): JiraAnalytics {
-  const now = new Date();
+  const now = getToday();
   let cutoffDate: Date;
 
   switch (period) {
     case '7d':
-      cutoffDate = new Date(now.getTime() - (7 * 24 * 60 * 60 * 1000));
+      cutoffDate = subtractDays(now, 7);
       break;
     case '30d':
-      cutoffDate = new Date(now.getTime() - (30 * 24 * 60 * 60 * 1000));
+      cutoffDate = subtractDays(now, 30);
       break;
     case '3m':
-      cutoffDate = new Date(now.getTime() - (90 * 24 * 60 * 60 * 1000));
+      cutoffDate = subtractDays(now, 90);
       break;
     case 'current':
     default:
@@ -56,7 +57,7 @@ function filterCurrentSprintAnalytics(analytics: JiraAnalytics): JiraAnalytics {
 function filterAnalyticsByDate(analytics: JiraAnalytics, cutoffDate: Date): JiraAnalytics {
   // Filtrer l'historique des sprints
   const filteredSprintHistory = analytics.velocityMetrics.sprintHistory.filter(sprint => {
-    const sprintEndDate = new Date(sprint.endDate);
+    const sprintEndDate = parseDate(sprint.endDate);
     return sprintEndDate >= cutoffDate;
   });