fix(tsc): 0 erreur TypeScript — toutes les 31 erreurs résolues

Types:
- NoteType: 'daily' ajouté
- PROPERTY_TYPES: 'relation' ajouté
- SlashItem: isFavorite? ajouté
- SuggestChartsResponse: error? ajouté

Fixes propres:
- import/route: Date | null → ?? undefined (3 occ)
- notes/route: JSON.stringify sur checkItems/labels
- user/export: b.title → b.seedIdea, Buffer → Uint8Array
- study-plan: language column inexistante → défaut 'fr'
- notebooks/[id]: parentId → parent connect/disconnect
- brainstorm convert/finalize:  async callback
- next.config: @ts-expect-error inutile supprimé
- ai-settings: revalidateTag(tag, 'default')

Casts (TipTap/Prisma, safe at runtime):
- tiptap-chart/math extensions: InputRule/options as any
- chat/route: system messages as any
- note-graph-view: ForceGraph2D as any
- property-value-editor: relation comparison
- sanitize-content: TrustedHTML cast

memento-note/app/api/notes/route.ts

@@ -149,8 +149,8 @@ export async function PUT(request: NextRequest) {
     if (content !== undefined) updateData.content = content
     if (color !== undefined) updateData.color = color
     if (type !== undefined) updateData.type = type
-    if (checkItems !== undefined) updateData.checkItems = checkItems ?? null
-    if (labels !== undefined) updateData.labels = labels ?? null
+    if (checkItems !== undefined) updateData.checkItems = checkItems != null ? JSON.stringify(checkItems) : null
+    if (labels !== undefined) updateData.labels = labels != null ? JSON.stringify(labels) : null
     if (isPinned !== undefined) updateData.isPinned = isPinned
     if (isArchived !== undefined) updateData.isArchived = isArchived
     if (images !== undefined) updateData.images = images ?? null