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/components/forms/CreateTaskForm.tsx

@@ -8,6 +8,7 @@ import { TagInput } from '@/components/ui/TagInput';
 import { TaskPriority, TaskStatus } from '@/lib/types';
 import { CreateTaskData } from '@/clients/tasks-client';
 import { getAllStatuses, getAllPriorities } from '@/lib/status-config';
+import { formatDateForDateTimeInput, parseDateTimeInput } from '@/lib/date-utils';
 
 interface CreateTaskFormProps {
   isOpen: boolean;
@@ -151,10 +152,10 @@ export function CreateTaskForm({ isOpen, onClose, onSubmit, loading = false }: C
         <Input
           label="Date d'échéance"
           type="datetime-local"
-          value={formData.dueDate ? new Date(formData.dueDate.getTime() - formData.dueDate.getTimezoneOffset() * 60000).toISOString().slice(0, 16) : ''}
+          value={formData.dueDate ? formatDateForDateTimeInput(formData.dueDate) : ''}
           onChange={(e) => setFormData((prev: CreateTaskData) => ({ 
             ...prev, 
-            dueDate: e.target.value ? new Date(e.target.value) : undefined 
+            dueDate: e.target.value ? parseDateTimeInput(e.target.value) : undefined 
           }))}
           disabled={loading}
         />

src/components/forms/EditTaskForm.tsx

@@ -11,6 +11,7 @@ import { Task, TaskPriority, TaskStatus } from '@/lib/types';
 import { useUserPreferences } from '@/contexts/UserPreferencesContext';
 // UpdateTaskData removed - using Server Actions directly
 import { getAllStatuses, getAllPriorities } from '@/lib/status-config';
+import { formatDateForDateTimeInput, parseDateTimeInput } from '@/lib/date-utils';
 
 interface EditTaskFormProps {
   isOpen: boolean;
@@ -56,7 +57,7 @@ export function EditTaskForm({ isOpen, onClose, onSubmit, task, loading = false
         status: task.status,
         priority: task.priority,
         tags: task.tags || [],
-        dueDate: task.dueDate ? new Date(task.dueDate) : undefined
+        dueDate: task.dueDate
       });
     }
   }, [task]);
@@ -181,10 +182,10 @@ export function EditTaskForm({ isOpen, onClose, onSubmit, task, loading = false
         <Input
           label="Date d'échéance"
           type="datetime-local"
-          value={formData.dueDate ? new Date(formData.dueDate.getTime() - formData.dueDate.getTimezoneOffset() * 60000).toISOString().slice(0, 16) : ''}
+          value={formData.dueDate ? formatDateForDateTimeInput(formData.dueDate) : ''}
           onChange={(e) => setFormData(prev => ({ 
             ...prev, 
-            dueDate: e.target.value ? new Date(e.target.value) : undefined 
+            dueDate: e.target.value ? parseDateTimeInput(e.target.value) : undefined 
           }))}
           disabled={loading}
         />

src/components/kanban/QuickAddTask.tsx

@@ -6,6 +6,7 @@ import { TagInput } from '@/components/ui/TagInput';
 import { TaskStatus, TaskPriority } from '@/lib/types';
 import { CreateTaskData } from '@/clients/tasks-client';
 import { getAllPriorities } from '@/lib/status-config';
+import { formatDateForDateTimeInput, parseDateTimeInput } from '@/lib/date-utils';
 
 interface QuickAddTaskProps {
   status: TaskStatus;
@@ -189,10 +190,10 @@ export function QuickAddTask({ status, onSubmit, onCancel, swimlaneContext }: Qu
         <div className="flex items-center justify-between text-xs min-w-0">
           <input
             type="datetime-local"
-            value={formData.dueDate ? new Date(formData.dueDate.getTime() - formData.dueDate.getTimezoneOffset() * 60000).toISOString().slice(0, 16) : ''}
+            value={formData.dueDate ? formatDateForDateTimeInput(formData.dueDate) : ''}
             onChange={(e) => setFormData(prev => ({ 
               ...prev, 
-              dueDate: e.target.value ? new Date(e.target.value) : undefined 
+              dueDate: e.target.value ? parseDateTimeInput(e.target.value) : undefined 
             }))}
             onFocus={() => setActiveField('date')}
             disabled={isSubmitting}

src/components/settings/BackupSettingsPageClient.tsx

@@ -194,7 +194,7 @@ export default function BackupSettingsPageClient({ initialData }: BackupSettings
 
   const formatDate = (date: string | Date): string => {
     // Format cohérent serveur/client pour éviter les erreurs d'hydratation
-    const d = typeof date === 'string' ? new Date(date) : date;
+    const d = typeof date === 'string' ? parseDate(date) : date;
     return formatDateForDisplay(d, 'DISPLAY_MEDIUM');
   };