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/providers-wrapper.tsx

@@ -9,6 +9,8 @@ import type { ReactNode } from 'react'
 import type { Translations } from '@/lib/i18n/load-translations'
 import { AiConsentProvider } from '@/components/legal/ai-consent-provider'
 import { SearchModalProvider } from '@/context/search-modal-context'
+import { OnboardingWizard } from '@/components/onboarding/onboarding-wizard'
+import { OnboardingEditorHints } from '@/components/onboarding/onboarding-editor-hints'
 
 const RTL_LANGUAGES = ['ar', 'fa']
 
@@ -42,6 +44,8 @@ export function ProvidersWrapper({
                 <DirWrapper>
                   <SearchModalProvider>
                     {children}
+                    <OnboardingWizard />
+                    <OnboardingEditorHints />
                   </SearchModalProvider>
                 </DirWrapper>
               </AiConsentProvider>