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/clients/daily-client.ts

@@ -1,6 +1,6 @@
 import { httpClient } from './base/http-client';
 import { DailyCheckbox, DailyView, Task } from '@/lib/types';
-import { formatDateForAPI, parseDate } from '@/lib/date-utils';
+import { formatDateForAPI, parseDate, getToday, addDays, subtractDays } from '@/lib/date-utils';
 
 // Types pour les réponses API (avec dates en string)
 interface ApiCheckbox {
@@ -74,7 +74,7 @@ export class DailyClient {
     
     const result = await httpClient.get<ApiHistoryItem[]>(`/daily?${params}`);
     return result.map(item => ({
-      date: new Date(item.date),
+      date: parseDate(item.date),
       checkboxes: item.checkboxes.map((cb: ApiCheckbox) => this.transformCheckboxDates(cb))
     }));
   }
@@ -128,16 +128,19 @@ export class DailyClient {
    * Récupère la vue daily d'une date relative (hier, aujourd'hui, demain)
    */
   async getDailyViewByRelativeDate(relative: 'yesterday' | 'today' | 'tomorrow'): Promise<DailyView> {
-    const date = new Date();
+    let date: Date;
     
     switch (relative) {
       case 'yesterday':
-        date.setDate(date.getDate() - 1);
+        date = subtractDays(getToday(), 1);
         break;
       case 'tomorrow':
-        date.setDate(date.getDate() + 1);
+        date = addDays(getToday(), 1);
+        break;
+      case 'today':
+      default:
+        date = getToday();
         break;
-      // 'today' ne change rien
     }
     
     return this.getDailyView(date);