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/prisma/migrations/20260529060000_add_onboarding_fields/migration.sql

@@ -0,0 +1,8 @@
+-- AddColumn: User.onboardingCompleted
+ALTER TABLE "User" ADD COLUMN IF NOT EXISTS "onboardingCompleted" BOOLEAN NOT NULL DEFAULT false;
+
+-- AddColumn: User.onboardingStep
+ALTER TABLE "User" ADD COLUMN IF NOT EXISTS "onboardingStep" INTEGER NOT NULL DEFAULT 0;
+
+-- AddColumn: Note.isDemo
+ALTER TABLE "Note" ADD COLUMN IF NOT EXISTS "isDemo" BOOLEAN NOT NULL DEFAULT false;

memento-note/prisma/schema.prisma

@@ -26,6 +26,8 @@ model User {
   updatedAt             DateTime                @updatedAt
   cardSizeMode          String                  @default("variable")
   accentColor           String                  @default("#A47148")
+  onboardingCompleted   Boolean                 @default(false)
+  onboardingStep        Int                     @default(0)
   accounts              Account[]
   agents                Agent[]
   aiFeedback            AiFeedback[]
@@ -175,6 +177,8 @@ model Note {
   historyEnabled             Boolean                  @default(false)
   /// URL d'origine pour les clips web (Web Clipper)
   sourceUrl                  String?
+  /// Note de démonstration insérée lors de l'onboarding
+  isDemo                     Boolean                  @default(false)
   /// Illustration SVG (sanitized) for editorial feed thumbnail — optional, peut être généré par IA
   illustrationSvg            String?
   tsv                        Unsupported("tsvector")?