feat: indicateur versioning sur cartes + toolbar éditeur

Note card:
- Icône History en overlay bottom-right (visible si historyEnabled=true)
- Discrète: text-muted-foreground/50, ne pollue pas l'UI
- Tooltip 'Historique des versions activé'

Toolbar éditeur:
- Icône History à côté du statut Saved/Dirty
- Visible seulement en sm+ (desktop)
- cursor-help + tooltip

i18n:
- notes.historyEnabledTooltip ajouté aux 15 locales (FR/EN traduits, 13 EN placeholder)

memento-note/components/note-editor/note-editor-toolbar.tsx

@@ -19,7 +19,7 @@ import { Badge } from '@/components/ui/badge'
 import {
   X, Plus, Palette, Image as ImageIcon, Bell, Eye, Link as LinkIcon, Sparkles,
   Maximize2, Copy, ArrowLeft, ChevronRight, PanelRight, Check, Loader2, Save, MoreHorizontal,
-  Trash2, LogOut, Wand2, Share2, Wind, Paperclip, GraduationCap, FileDown, FileUp, Mic, MicOff, Printer, PenTool, Loader2 as Loader2Icon, Globe, ExternalLink
+  Trash2, LogOut, Wand2, Share2, Wind, Paperclip, GraduationCap, FileDown, FileUp, Mic, MicOff, Printer, PenTool, Loader2 as Loader2Icon, Globe, ExternalLink, History
 } from 'lucide-react'
 import { FlashcardGenerateDialog } from '@/components/flashcards/flashcard-generate-dialog'
 import { NoteShareDialog } from './note-share-dialog'
@@ -549,6 +549,15 @@ export function NoteEditorToolbar({ mode, onClose, onToggleAttachments, attachme
               : <><Check className="h-3 w-3 text-emerald-500" /><span>{t('notes.savedStatus')}</span></>}
           </span>
 
+          {note.historyEnabled && (
+            <span
+              className="hidden sm:flex items-center gap-1 text-[11px] text-foreground/35 select-none cursor-help"
+              title={t('notes.historyEnabledTooltip') || 'Version history enabled'}
+            >
+              <History className="h-3 w-3" />
+            </span>
+          )}
+
           {state.isMarkdown && !readOnly && (
             <button
               title={state.showMarkdownPreview ? t('notes.markdownEditingTitle') : t('notes.markdownPreviewTitle')}