refactor(i18n) : replace hardcoded French strings with i18n keys

Replace 30+ hardcoded strings across 15 components with $t() calls.
Added keys for common actions, drawers titles, empty states, and modals.

Ticket: T-020

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/components/task/TaskModal.vue

@@ -24,7 +24,7 @@
                                     {{ task.project.code }}-{{ task.number }}
                                 </span>
                                 <h2 class="text-lg font-bold tracking-tight text-neutral-900">
-                                    {{ isEditing ? 'Modifier un ticket' : 'Ajouter un ticket' }}
+                                    {{ isEditing ? $t('tasks.editTask') : $t('tasks.addTask') }}
                                 </h2>
                             </div>
                             <button
@@ -568,7 +568,7 @@ async function handleArchive() {
     if (timerStore.activeEntry?.task) {
         const taskIri = typeof timerStore.activeEntry.task === 'string'
             ? timerStore.activeEntry.task
-            : (timerStore.activeEntry.task as any)?.['@id'] ?? `/api/tasks/${(timerStore.activeEntry.task as any)?.id}`
+            : (timerStore.activeEntry.task as Task)?.['@id'] ?? `/api/tasks/${(timerStore.activeEntry.task as Task)?.id}`
         if (taskIri === `/api/tasks/${props.task.id}`) {
             await timerStore.stop()
         }