fix: exercices dans panneau IA + erreur language

- Générateur d'exercices déplacé du menu ⋯ vers le panneau IA (onglet Actions > Outils de génération)
- Même design que les cartes slides/diagrammes
- Fix: import useLanguage supprimé de la route API (hook client en serveur)
- i18n FR/EN

memento-note/locales/en.json

@@ -2561,6 +2561,11 @@
     "generateExercises": "Generate exercises",
     "exercisesLoading": "Generating exercises...",
     "exercisesGenerated": "exercises created!",
+    "aiGenerateExercises": "Generate exercises",
+    "aiGenerateExercisesHint": "5 exercises with answers",
+    "aiGenerateExercisesDesc": "AI creates 5 exercises based on this note, with varied difficulty levels and detailed answers.",
+    "aiGenerateExercisesCreated": "exercises created!",
+    "aiGenerateGenerateExercises": "Generate",
     "wizardStudyPlanner": "Study Plan",
     "wizardStudyPlannerDesc": "AI creates a revision plan based on spaced repetition.",
     "wizardExamDate": "Exam date",