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/components/brainstorm/activity-feed.tsx

@@ -40,7 +40,7 @@ function getActionLabel(action: string, t: (key: string) => string | undefined):
 function timeAgo(dateStr: string, t: (key: string) => string | undefined): string {
   const diff = Date.now() - new Date(dateStr).getTime()
   const mins = Math.floor(diff / 60000)
-  if (mins < 1) return t('brainstorm.justNow')
+  if (mins < 1) return t('brainstorm.justNow') || ''
   if (mins < 60) return `${mins}m`
   const hours = Math.floor(mins / 60)
   if (hours < 24) return `${hours}h`