refactor: clean up codebase, remove dead code and obsolete docs

Remove influencer-era documentation, unused components, boilerplate
assets, and ghost tiktok cron job. Add supplier invoice management,
document API routes, and PWA icons. Replace boilerplate README.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

components/ui/empty-state.tsx

@@ -100,14 +100,14 @@ export function EmptyInvoices() {
   )
 }
 
-export function EmptyCustomers() {
+export function EmptyCustomers({ onAction }: { onAction?: () => void } = {}) {
   return (
     <EmptyState
       icon={Users}
       title="Inga kunder ännu"
       description="Lägg till dina kunder för att enkelt skapa fakturor och hålla koll på betalningar."
       actionLabel="Lägg till kund"
-      actionHref="/customers/new"
+      onAction={onAction}
     />
   )
 }