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/locales/en.json

@@ -2429,7 +2429,12 @@
       "Italiano": "Italian",
       "Chinois": "Chinese",
       "Japonais": "Japanese"
-    }
+    },
+    "exportMarkdown": "Export as Markdown",
+    "importMarkdown": "Import Markdown",
+    "markdownExportSuccess": "Note exported as Markdown",
+    "markdownExportError": "Failed to export note",
+    "markdownImportSuccess": "Markdown imported successfully"
   },
   "flashcards": {
     "generateTitle": "Generate flashcards",
@@ -2495,7 +2500,7 @@
     "retentionRate": "Retention rate",
     "masteredLabel": "{count}/{total} mastered",
     "retentionCurve": "Weekly success rate",
-    "retentionCurveHint": "Based on reviews with grade \u2265 Good (3 or 4)",
+    "retentionCurveHint": "Based on reviews with grade ≥ Good (3 or 4)",
     "retentionNoDataYet": "Review more cards across multiple weeks to see your retention curve.",
     "streak": "Current streak",
     "streakDays": "days",
@@ -2792,7 +2797,16 @@
     "ideasCount": "ideas",
     "star": "Star idea",
     "unstar": "Unstar idea",
-    "renameSession": "Rename session"
+    "renameSession": "Rename session",
+    "downloadPptx": "PPTX",
+    "downloadPptxDesc": "Download as PowerPoint",
+    "pptxSuccess": "PPTX downloaded",
+    "pptxError": "PPTX export failed",
+    "fitToScreen": "Re-center",
+    "legendWave1": "Variations",
+    "legendWave2": "Analogies",
+    "legendWave3": "Disruptions",
+    "legendConverted": "Converted"
   },
   "byokSettings": {
     "title": "Your API keys (BYOK)",
@@ -3461,5 +3475,96 @@
     "notesLoadError": "Error loading notes",
     "defaultOption1": "Option 1",
     "defaultOption2": "Option 2"
+  },
+  "onboarding": {
+    "welcome_title": "Your AI-augmented memory",
+    "welcome_subtitle": "Momento remembers what you forget.",
+    "welcome_cta": "Get started",
+    "skip": "Skip",
+    "step_notes_title": "Your notes",
+    "step_notes_empty": "You have no notes yet. Import yours or start with examples.",
+    "step_notes_import": "Import my notes",
+    "step_notes_demo": "Create 5 example notes",
+    "step_notes_has_notes": "You already have {count} notes. Let's discover the magic.",
+    "step_notes_cta": "My notes are ready",
+    "step_aha_title": "Find what you forgot",
+    "step_aha_subtitle": "Type a question. Find a note you forgot.",
+    "step_aha_placeholder": "notes about productivity...",
+    "step_aha_cta": "Explore Momento",
+    "progress": "{current} of {total}",
+    "creating_demo_notes": "Creating example notes...",
+    "demo_notes_ready": "5 example notes created!",
+    "badge_credits": "⚡ {count} credits left",
+    "badge_upgrade": "Upgrade to Pro →",
+    "no_results": "No results — try another query.",
+    "search_credit_used": "1 search used",
+    "quota_exceeded": "Search quota reached — upgrade to Pro for unlimited.",
+    "step_aha_search_button": "Search",
+    "step_aha_search_aria": "Search your notes",
+    "step_notes_hint": "💡 These notes will power the AI search demo in the next step.",
+    "step_features_title": "Your AI superpowers",
+    "step_features_subtitle": "Choose where to start.",
+    "step_features_cta": "Let's go!",
+    "feature_search_title": "Semantic search",
+    "feature_search_desc": "Find any note by meaning, not just keywords.",
+    "feature_flashcards_title": "AI Flashcards",
+    "feature_flashcards_desc": "Generate SRS review cards from your notes in one click.",
+    "feature_brainstorm_title": "AI Brainstorm",
+    "feature_brainstorm_desc": "AI-powered collaborative brainstorming sessions.",
+    "feature_chat_title": "Chat with your notes",
+    "feature_chat_desc": "Ask questions to your personal knowledge base.",
+    "feature_insights_title": "Semantic insights",
+    "feature_insights_desc": "Discover hidden connections between your ideas.",
+    "feature_export_title": "Markdown export",
+    "feature_export_desc": "Import and export your notes in standard Markdown format.",
+    "welcome_title_name": "Hello {name} 👋",
+    "import_formats": "Accepted formats: .md, .txt",
+    "import_error": "Could not import some files. Please try again.",
+    "import_notes_ready": "{count} note(s) imported!",
+    "action_write_title": "Write your first real note",
+    "action_write_desc": "Create a note and start capturing your ideas.",
+    "action_flashcards_title": "Generate your first flashcards",
+    "action_flashcards_desc": "Open a note and click the flashcards button.",
+    "action_brainstorm_title": "Start an AI brainstorm",
+    "action_brainstorm_desc": "Explore your ideas with a dedicated AI agent.",
+    "action_try": "Try",
+    "step_features_cta_all": "All done — let's dive in!",
+    "action_write_where": "Close this → click \"+ New note\" in the sidebar",
+    "action_flashcards_where": "Close this → open a note → 🃏 button in the toolbar",
+    "action_brainstorm_where": "Close this → \"Canvas\" section in the sidebar",
+    "pill_resume": "✨ Resume tour",
+    "action_done": "Tried!",
+    "editor_hints_title": "Editor tips",
+    "editor_hints_got_it": "Got it!",
+    "hint_slash_title": "\"/\" command — insert blocks",
+    "hint_slash_desc": "In the editor, type \"/\" to open the block menu: heading, list, code block, table, to-do list, and AI commands (Clarify, Shorten, Improve, Expand).",
+    "hint_ai_title": "Built-in AI assistant",
+    "hint_ai_desc": "Click the ✨ button in the toolbar to open the AI panel — ask questions, summarize, rewrite, or brainstorm directly in your note.",
+    "hint_version_title": "Version history",
+    "hint_version_desc": "Click the ⓘ button in the toolbar → \"Versions\" tab. Enable versioning, then save and restore snapshots of your note at any time.",
+    "hint_flashcards_title": "Generate flashcards",
+    "hint_flashcards_desc": "Click the 🎓 button in the toolbar to auto-generate flashcards from your note for spaced repetition review.",
+    "hint_links_title": "Links between notes",
+    "hint_links_desc": "Type \"[[\" in the editor to search and link to another note. Linked notes appear as backlinks at the bottom of the note.",
+    "hint_create_note_title": "Create a note",
+    "hint_create_note_desc": "Click the \"+\" button in the sidebar or press Ctrl+N to create a new note. Then start writing.",
+    "hint_flip_title": "Flip the card",
+    "hint_flip_desc": "Press Space (or click the card) to flip it and reveal the answer.",
+    "hint_rate_keys_title": "Rate with keyboard",
+    "hint_rate_keys_desc": "After flipping, press 1 (Hard), 2 (Difficult), 3 (Good) or 4 (Easy) to rate the card. The SM-2 algorithm schedules your next review automatically.",
+    "hint_generate_from_note_title": "Generate from a note",
+    "hint_generate_from_note_desc": "Open any note and click the 🎓 button in the toolbar to automatically generate flashcards from its content.",
+    "hint_brainstorm_start_title": "Start with an idea",
+    "hint_brainstorm_start_desc": "Type any concept or question in the input field and press Enter. The AI will generate a set of ideas around it.",
+    "hint_brainstorm_deepen_title": "Deepen an idea",
+    "hint_brainstorm_deepen_desc": "Click on any idea card to expand it with sub-ideas and explore it further.",
+    "hint_brainstorm_export_title": "Export your session",
+    "hint_brainstorm_export_desc": "When done, export the entire brainstorm session as a structured note saved to your notebook.",
+    "hint_insights_clusters_title": "Note clusters",
+    "hint_insights_clusters_desc": "Your notes are automatically grouped into thematic clusters. Click a cluster to explore the notes it contains.",
+    "hint_insights_bridge_title": "Bridge notes",
+    "hint_insights_bridge_desc": "Bridge notes connect multiple clusters. They are highlighted because they hold your knowledge graph together.",
+    "hint_insights_refresh_title": "Refresh clusters",
+    "hint_insights_refresh_desc": "If you've added new notes, click the refresh button to recalculate the clusters with the latest content."
   }
 }