feat: update dashboard components and analytics for 7-day summaries

- Modified `ManagerWeeklySummary`, `MetricsTab`, and `ProductivityAnalytics` to reflect a focus on the last 7 days instead of the current week.
- Enhanced `ManagerSummaryService` and `MetricsService` to calculate metrics over a sliding 7-day window, improving data relevance.
- Added a new utility function `formatDistanceToNow` for better date formatting in French.
- Updated comments and documentation to clarify changes in timeframes.

src/lib/date-utils.ts

@@ -3,7 +3,7 @@
  * Regroupe toutes les fonctions de formatage, manipulation et validation de dates
  */
 
-import { format, startOfDay, endOfDay, isValid } from 'date-fns';
+import { format, startOfDay, endOfDay, isValid, formatDistanceToNow as formatDistanceToNowFns } from 'date-fns';
 import { fr } from 'date-fns/locale';
 
 // Re-export des utilitaires workday existants
@@ -244,3 +244,17 @@ export function generateDateTitle(date: Date, emoji: string = '📅'): string {
   
   return `${emoji} ${formatDateShort(date)}`;
 }
+
+/**
+ * Formate la distance depuis maintenant en français
+ */
+export function formatDistanceToNow(date: Date, options?: { addSuffix?: boolean }): string {
+  if (!isValid(date)) {
+    throw new Error('Date invalide fournie à formatDistanceToNow');
+  }
+  
+  return formatDistanceToNowFns(date, {
+    locale: fr,
+    addSuffix: options?.addSuffix ?? true
+  });
+}