fix: increase reformulate word limit to 2000 + i18n error messages

- Raise MAX_WORDS from 500 to 2000 for text reformulation
- Error messages now use i18n keys (ai.wordCountMin/Max) instead of
  hardcoded English strings
- Client translates server errors using the user's UI language

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/locales/en.json

@@ -376,6 +376,8 @@
     "undoAI": "Undo AI transformation",
     "undoApplied": "Original text restored",
     "minWordsError": "Note must contain at least 5 words to use AI actions.",
+    "wordCountMin": "Please select at least {min} words to reformulate (currently {current} words)",
+    "wordCountMax": "Please select at most {max} words to reformulate (currently {current} words)",
     "genericError": "AI error",
     "actionError": "Error during AI action",
     "appliedToNote": "Applied to note",

memento-note/locales/fr.json

@@ -376,6 +376,8 @@
     "undoAI": "Annuler la transformation IA",
     "undoApplied": "Texte original restauré",
     "minWordsError": "La note doit contenir au moins 5 mots pour utiliser les actions IA.",
+    "wordCountMin": "Veuillez sélectionner au moins {min} mots pour reformuler ({current} mots sélectionnés)",
+    "wordCountMax": "Veuillez sélectionner au maximum {max} mots pour reformuler ({current} mots sélectionnés)",
     "genericError": "Erreur IA",
     "actionError": "Erreur lors de l'action IA",
     "appliedToNote": "Appliqué à la note",