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/TaskDrawer.vue

@@ -1,5 +1,5 @@
 <template>
-    <AppDrawer v-model="isOpen" :title="isEditing ? 'Modifier un ticket' : 'Ajouter un ticket'">
+    <AppDrawer v-model="isOpen" :title="isEditing ? $t('tasks.editTask') : $t('tasks.addTask')">
         <form @submit.prevent="handleSubmit" class="flex flex-col gap-2">
             <MalioInputText
                 v-model="form.title"
@@ -267,7 +267,7 @@ async function handleArchive() {
     if (timerStore.activeEntry?.task) {
         const taskIri = typeof timerStore.activeEntry.task === 'string'
             ? timerStore.activeEntry.task
-            : (timerStore.activeEntry.task as any)?.['@id'] ?? `/api/tasks/${(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()
         }