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/onboarding/starter-pack-badge.tsx

@@ -0,0 +1,59 @@
+'use client'
+
+import { useQuery } from '@tanstack/react-query'
+import { Zap, ArrowUpRight } from 'lucide-react'
+import { cn } from '@/lib/utils'
+import { useLanguage } from '@/lib/i18n'
+import Link from 'next/link'
+
+interface QuotaData { remaining: number; limit: number; used: number }
+interface UsageData { quotas: Record<string, QuotaData>; tier: string }
+
+export function StarterPackBadge() {
+  const { t } = useLanguage()
+
+  const { data } = useQuery<UsageData>({
+    queryKey: ['usage', 'current'],
+    queryFn: async () => {
+      const res = await fetch('/api/usage/current')
+      if (!res.ok) throw new Error('Failed')
+      return res.json()
+    },
+    staleTime: 5000,
+  })
+
+  if (!data) return null
+  // Paid tiers do not need the badge; only BASIC (free) users see it
+  const PAID_TIERS = ['PRO', 'BUSINESS', 'ENTERPRISE']
+  if (PAID_TIERS.includes(data.tier)) return null
+
+  const semanticQuota = data.quotas?.['semantic_search']
+  if (!semanticQuota) return null
+
+  const remaining = semanticQuota.remaining ?? 0
+  const isCritical = remaining === 0
+  const isWarning = remaining > 0 && remaining < 5
+
+  return (
+    <Link
+      href="/pricing"
+      className={cn(
+        'flex items-center gap-2 rounded-lg px-3 py-2 text-xs font-medium transition-colors',
+        isCritical
+          ? 'bg-destructive/10 text-destructive hover:bg-destructive/20'
+          : isWarning
+            ? 'bg-orange-500/10 text-orange-500 hover:bg-orange-500/20'
+            : 'bg-muted text-muted-foreground hover:text-foreground hover:bg-muted/80'
+      )}
+    >
+      <Zap className={cn('h-3.5 w-3.5', isWarning || isCritical ? 'animate-pulse' : '')} />
+      <span>
+        {isCritical
+          ? t('onboarding.badge_upgrade')
+          : t('onboarding.badge_credits', { count: remaining })
+        }
+      </span>
+      {isCritical && <ArrowUpRight className="h-3 w-3 ml-auto" />}
+    </Link>
+  )
+}