Epic 6: Stories 6-2 (Markdown roundtrip) + 6-3 (Brainstorm PPTX + Canvas)

Story 6-2 — Markdown roundtrip export/import:
- lib/editor/markdown-export.ts: tiptapHTMLToMarkdown, markdownToHTML, looksLikeMarkdown
- lib/editor/markdown-paste-extension.ts: TipTap extension paste Markdown → blocs
- note-editor-toolbar.tsx: export .md + import .md (file picker)
- rich-text-editor.tsx: intégration MarkdownPasteExtension
- 40 tests unitaires markdown-export.test.ts

Story 6-3 — Brainstorm PPTX + Canvas:
- lib/brainstorm/export-pptx.ts: génération PPTX 5 slides (pptxgenjs)
- app/api/brainstorm/[sessionId]/export-pptx/route.ts: route POST protégée
- brainstorm-page.tsx: bouton PPTX, auto-select session, fix emoji, fix router.replace
- wave-canvas.tsx: fitTrigger recentrage, légende bas-droite

Onboarding activation wizard (Story 6-1):
- components/onboarding/: wizard multi-étapes, hints éditeur
- app/api/onboarding/: route PATCH onboarding
- prisma/migrations: champs onboarding user

Locales: 15 langues mises à jour (brainstorm, markdown, onboarding keys)
Sprint: 6-1 done, 6-2 review, 6-3 review

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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

@@ -11,6 +11,7 @@ import {
   DropdownMenu,
   DropdownMenuContent,
   DropdownMenuItem,
+  DropdownMenuSeparator,
   DropdownMenuTrigger,
 } from '@/components/ui/dropdown-menu'
 import { Button } from '@/components/ui/button'
@@ -18,7 +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
+  Trash2, LogOut, Wand2, Share2, Wind, Paperclip, GraduationCap, FileDown, FileUp
 } from 'lucide-react'
 import { FlashcardGenerateDialog } from '@/components/flashcards/flashcard-generate-dialog'
 import { NoteShareDialog } from './note-share-dialog'
@@ -29,6 +30,7 @@ import { NOTE_COLORS, NoteColor, Note } from '@/lib/types'
 import { cn } from '@/lib/utils'
 import { toast } from 'sonner'
 import { format } from 'date-fns'
+import { tiptapHTMLToMarkdown, markdownToHTML, extractMarkdownTitle } from '@/lib/editor/markdown-export'
 
 interface NoteEditorToolbarProps {
   mode: 'fullPage' | 'dialog'
@@ -38,16 +40,70 @@ interface NoteEditorToolbarProps {
 }
 
 export function NoteEditorToolbar({ mode, onClose, onToggleAttachments, attachmentsCount }: NoteEditorToolbarProps) {
-  const { state, actions, note, readOnly, fullPage, notebooks, fileInputRef } = useNoteEditorContext()
+  const { state, actions, note, readOnly, fullPage, notebooks, fileInputRef, richTextEditorRef } = useNoteEditorContext()
   const { t } = useLanguage()
   const [isConverting, setIsConverting] = useState(false)
   const [shareOpen, setShareOpen] = useState(false)
   const [flashcardsOpen, setFlashcardsOpen] = useState(false)
+  const mdImportInputRef = useRef<HTMLInputElement>(null)
 
   const notebookName = notebooks.find(nb => nb.id === note.notebookId)?.name || null
 
   const undoSnapshotRef = useRef<{ content: string; isMarkdown: boolean } | null>(null)
 
+  // ── Markdown export ───────────────────────────────────────────────────────
+  const handleExportMarkdown = () => {
+    try {
+      const editor = richTextEditorRef?.current?.getEditor()
+      if (!editor) {
+        toast.error(t('richTextEditor.markdownExportError'))
+        return
+      }
+      const html = editor.getHTML()
+      const title = state.title || note.title || 'note'
+      const titleLine = title ? `# ${title}\n\n` : ''
+      const markdown = titleLine + tiptapHTMLToMarkdown(html)
+      const blob = new Blob([markdown], { type: 'text/markdown;charset=utf-8' })
+      const url = URL.createObjectURL(blob)
+      const a = document.createElement('a')
+      a.href = url
+      a.download = `${title.replace(/[^a-z0-9\-_\s]/gi, '').trim().replace(/\s+/g, '-') || 'note'}.md`
+      document.body.appendChild(a)
+      a.click()
+      document.body.removeChild(a)
+      URL.revokeObjectURL(url)
+      toast.success(t('richTextEditor.markdownExportSuccess'))
+    } catch {
+      toast.error(t('richTextEditor.markdownExportError'))
+    }
+  }
+
+  // ── Markdown import ───────────────────────────────────────────────────────
+  const handleImportMarkdownFile = (e: React.ChangeEvent<HTMLInputElement>) => {
+    const file = e.target.files?.[0]
+    if (!file) return
+    const reader = new FileReader()
+    reader.onload = (ev) => {
+      try {
+        const md = ev.target?.result as string
+        const html = markdownToHTML(md)
+        const extractedTitle = extractMarkdownTitle(md)
+        const editor = richTextEditorRef?.current?.getEditor()
+        if (editor) {
+          editor.commands.setContent(html)
+        }
+        actions.setContent(html)
+        if (extractedTitle) actions.setTitle(extractedTitle)
+        toast.success(t('richTextEditor.markdownImportSuccess'))
+      } catch {
+        toast.error(t('richTextEditor.markdownExportError'))
+      }
+    }
+    reader.readAsText(file)
+    // Reset input so same file can be imported again
+    e.target.value = ''
+  }
+
   const handleConvertToRichtext = async () => {
     if (isConverting || !state.content.trim()) return
     setIsConverting(true)
@@ -240,7 +296,16 @@ export function NoteEditorToolbar({ mode, onClose, onToggleAttachments, attachme
                   <MoreHorizontal size={16} />
                 </button>
               </DropdownMenuTrigger>
-              <DropdownMenuContent align="end" className="w-48">
+              <DropdownMenuContent align="end" className="w-52">
+                <DropdownMenuItem onClick={handleExportMarkdown}>
+                  <FileDown className="h-4 w-4 me-2" />
+                  {t('richTextEditor.exportMarkdown')}
+                </DropdownMenuItem>
+                <DropdownMenuItem onClick={() => mdImportInputRef.current?.click()}>
+                  <FileUp className="h-4 w-4 me-2" />
+                  {t('richTextEditor.importMarkdown')}
+                </DropdownMenuItem>
+                <DropdownMenuSeparator />
                 <DropdownMenuItem
                   onClick={async () => {
                     try {
@@ -304,6 +369,7 @@ export function NoteEditorToolbar({ mode, onClose, onToggleAttachments, attachme
   }
 
   return (
+    <>
     <div className="flex items-center justify-between pt-3 border-t border-border/30">
       <div className="flex items-center gap-0.5">
         {!readOnly && (
@@ -432,5 +498,14 @@ export function NoteEditorToolbar({ mode, onClose, onToggleAttachments, attachme
         )}
       </div>
     </div>
+    {/* Hidden file input for Markdown import */}
+    <input
+      ref={mdImportInputRef}
+      type="file"
+      accept=".md,text/markdown"
+      className="hidden"
+      onChange={handleImportMarkdownFile}
+    />
+    </>
   )
 }