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/auth.ts

@@ -55,8 +55,9 @@ export const { auth, signIn, signOut, handlers } = NextAuth({
       return true;
     },
     async jwt({ token, user, trigger, session }) {
-      if (trigger === 'update' && session && 'aiSessionConsent' in session) {
-        token.aiSessionConsent = session.aiSessionConsent === true;
+      if (trigger === 'update' && session) {
+        if ('aiSessionConsent' in session) token.aiSessionConsent = session.aiSessionConsent === true;
+        if ('onboardingCompleted' in session) token.onboardingCompleted = session.onboardingCompleted === true;
         return token;
       }
       if (user?.id) {
@@ -64,15 +65,16 @@ export const { auth, signIn, signOut, handlers } = NextAuth({
         token.aiSessionConsent = false;
         const dbUser = await prisma.user.findUnique({
           where: { id: user.id },
-          select: { role: true, sessionVersion: true },
+          select: { role: true, sessionVersion: true, onboardingCompleted: true },
         });
         if (!dbUser) return null;
         token.role = dbUser.role;
         token.sessionVersion = dbUser.sessionVersion;
+        token.onboardingCompleted = dbUser.onboardingCompleted;
       } else if (token.sub) {
         const dbUser = await prisma.user.findUnique({
           where: { id: token.sub },
-          select: { role: true, sessionVersion: true },
+          select: { role: true, sessionVersion: true, onboardingCompleted: true },
         });
         if (!dbUser) return null;
         if (
@@ -84,6 +86,7 @@ export const { auth, signIn, signOut, handlers } = NextAuth({
         token.id = token.sub;
         token.role = dbUser.role;
         token.sessionVersion = dbUser.sessionVersion;
+        token.onboardingCompleted = dbUser.onboardingCompleted;
       }
       return token;
     },