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/ui/ConfirmDeleteStatusModal.vue

@@ -4,19 +4,18 @@
             <div class="fixed inset-0 z-50 flex items-center justify-center">
                 <div class="absolute inset-0 bg-black/30" @click="cancel" />
                 <div class="relative z-10 w-full max-w-md rounded-lg bg-white p-6 shadow-xl">
-                    <h3 class="text-lg font-bold text-neutral-900">Supprimer le statut « {{ statusLabel }} »</h3>
+                    <h3 class="text-lg font-bold text-neutral-900">{{ $t('taskStatuses.deleteStatus', { label: statusLabel }) }}</h3>
 
                     <p class="mt-3 text-sm text-neutral-600">
-                        {{ taskCount }} tâche{{ taskCount > 1 ? 's sont liées' : ' est liée' }} à ce statut.
-                        Choisissez où les déplacer :
+                        {{ taskCount > 1 ? $t('taskStatuses.linkedTasksPlural', { count: taskCount }) : $t('taskStatuses.linkedTasks', { count: taskCount }) }}
                     </p>
 
                     <div class="mt-4">
                         <MalioSelect
                             v-model="targetStatusId"
                             :options="targetOptions"
-                            label="Déplacer vers"
-                            empty-option-label="Backlog (sans statut)"
+                            :label="$t('taskStatuses.moveTo')"
+                            :empty-option-label="$t('taskStatuses.backlog')"
                             min-width="w-full"
                         />
                     </div>
@@ -27,7 +26,7 @@
                             class="rounded-md border border-neutral-300 px-4 py-2 text-sm font-semibold text-neutral-700 hover:bg-neutral-50"
                             @click="cancel"
                         >
-                            Annuler
+                            {{ $t('common.cancel') }}
                         </button>
                         <button
                             type="button"
@@ -35,7 +34,7 @@
                             :disabled="isProcessing"
                             @click="confirm"
                         >
-                            Supprimer
+                            {{ $t('common.delete') }}
                         </button>
                     </div>
                 </div>