fix(frontend): i18n reactive badges + aria-labels + ExportEngagementButton + noMatch (review polish)

- ExportEngagementButton: full i18n (export.btn, export.btnLoading, export.aria)
- Layout: aria-label nav.brandHome on brand link, nav.themeAria on theme button
- SimulationList: aria-label simulation.list.rowActions on chevron button
- C2TasksPanel: aria-label c2.tasks.col.expand on expand column header
- ImportC2HistoryModal: aria-label common.select on select column header
- MitreMatrixModal: common.collapse/expand interpolated aria-label + mitre.matrix.noMatch
- fr.json: new keys common.expand/collapse/select, nav.brandHome/themeAria, export.*, simulation.list.rowActions, mitre.matrix.noMatch, c2.tasks.col.expand

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/i18n/fr.json

@@ -16,7 +16,10 @@
     "close": "Fermer",
     "confirm": "Confirmer",
     "yes": "Oui",
-    "no": "Non"
+    "no": "Non",
+    "expand": "Déplier {{id}}",
+    "collapse": "Replier {{id}}",
+    "select": "Sélectionner"
   },
   "nav": {
     "engagements": "Engagements",
@@ -24,8 +27,15 @@
     "users": "Utilisateurs",
     "signOut": "Se déconnecter",
     "brand": "Mimic",
+    "brandHome": "Accueil Mimic",
+    "themeAria": "Thème : {{label}} — cliquer pour changer",
     "footer": "Mimic — Outillage interne Purple Team. Engagements autorisés uniquement."
   },
+  "export": {
+    "btn": "Exporter",
+    "btnLoading": "Export en cours…",
+    "aria": "Options d'export"
+  },
   "auth": {
     "login": {
       "title": "Mimic",
@@ -208,7 +218,8 @@
         "desc": "Créez votre première simulation pour cet engagement."
       },
       "new": "Nouvelle simulation",
-      "error": "Impossible de charger les simulations"
+      "error": "Impossible de charger les simulations",
+      "rowActions": "Plus d'options"
     }
   },
   "template": {
@@ -382,7 +393,8 @@
         "command": "Commande",
         "source": "Source",
         "status": "Statut",
-        "completedAt": "Terminé le"
+        "completedAt": "Terminé le",
+        "expand": "Déplier"
       },
       "refreshing": "Actualisation…"
     },
@@ -464,7 +476,8 @@
       "applyItem_other": "Appliquer ({{count}} éléments)",
       "clearAll": "Tout effacer",
       "close": "Fermer",
-      "retry": "Réessayer"
+      "retry": "Réessayer",
+      "noMatch": "Aucun résultat"
     },
     "field": {
       "empty": "Aucune technique associée.",