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/time-tracking/TimeEntryList.vue

@@ -1,7 +1,7 @@
 <template>
     <div class="space-y-2">
         <div v-if="entries.length === 0" class="rounded-lg border border-neutral-200 bg-neutral-50 py-12 text-center text-sm text-neutral-400">
-            Aucune activité pour cette période
+            {{ $t('timeEntries.noEntries') }}
         </div>
 
         <div
@@ -20,7 +20,7 @@
             <div class="min-w-0 flex-1">
                 <div class="flex items-center gap-2">
                     <span class="truncate text-sm font-semibold text-neutral-900">
-                        {{ entry.title || 'Sans titre' }}
+                        {{ entry.title || $t('common.untitled') }}
                     </span>
                     <span
                         v-for="tag in entry.tags"
@@ -56,7 +56,7 @@
             <!-- Delete action -->
             <button
                 class="shrink-0 rounded-md p-1.5 text-neutral-300 opacity-0 transition hover:bg-red-50 hover:text-red-500 group-hover:opacity-100"
-                title="Supprimer"
+                :title="$t('common.delete')"
                 @click.stop="emit('deleteEntry', entry)"
             >
                 <Icon name="mdi:delete-outline" size="18" />