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>

docs/sprint-status.yaml

@@ -61,4 +61,13 @@ development_status:
   epic-5: in-progress
   5-1-nextgen-editor: done
 
+  # Epic 6 — Croissance & Activation (PLG) — ajouté 2026-05-29
+  epic-6: in-progress
+  6-1-onboarding-activation: done             # story-onboarding-activation.md
+  6-2-markdown-roundtrip: review        # brief-markdown-roundtrip.md
+  6-3-brainstorm-canvas-finalize: review        # story: 6-3-brainstorm-canvas-finalize.md
+  6-4-chat-with-pdf: backlog
+  6-5-pptx-export-watermark: backlog
+  epic-6-retrospective: optional
+