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/app/api/user/me/route.ts

@@ -0,0 +1,61 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { auth } from '@/auth'
+import prisma from '@/lib/prisma'
+
+/**
+ * GET /api/user/me
+ * Returns lightweight user profile including onboardingCompleted flag.
+ */
+export async function GET() {
+  const session = await auth()
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
+  const user = await prisma.user.findUnique({
+    where: { id: session.user.id },
+    select: { id: true, name: true, email: true, onboardingCompleted: true, onboardingStep: true },
+  })
+  if (!user) return NextResponse.json({ error: 'User not found' }, { status: 404 })
+  return NextResponse.json(user)
+}
+
+/**
+ * PATCH /api/user/me
+ * Partial update of user profile. Supported fields: onboardingCompleted, onboardingStep.
+ */
+export async function PATCH(req: NextRequest) {
+  const session = await auth()
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
+  let body: Record<string, unknown>
+  try {
+    body = await req.json()
+  } catch {
+    return NextResponse.json({ error: 'Invalid JSON' }, { status: 400 })
+  }
+
+  const allowedFields = ['onboardingCompleted', 'onboardingStep'] as const
+  type AllowedField = typeof allowedFields[number]
+  const data: Partial<Record<AllowedField, unknown>> = {}
+  if ('onboardingCompleted' in body) {
+    data.onboardingCompleted = Boolean(body.onboardingCompleted)
+  }
+  if ('onboardingStep' in body) {
+    const val = parseInt(String(body.onboardingStep), 10)
+    if (Number.isInteger(val) && val >= 0 && val <= 10) {
+      data.onboardingStep = val
+    }
+  }
+
+  if (Object.keys(data).length === 0) {
+    return NextResponse.json({ error: 'No valid fields to update' }, { status: 400 })
+  }
+
+  const updated = await prisma.user.update({
+    where: { id: session.user.id },
+    data: data as any,
+    select: { id: true, onboardingCompleted: true, onboardingStep: true },
+  })
+  return NextResponse.json(updated)
+}