feat: add mobile-first Creator Dashboard with charts

Commit notes

- Add dashboard API endpoint with stats, sales chart, top packs, and recent sales - Create Creator Dashboard page with Chart.js for sales visualization - Add Mollie Connect onboarding card for automatic seller payouts - Add StatCard, SalesChart, RecentSalesList, TopPacksList components - Add MollieConnectCard component for seller onboarding status - Add dashboard link to header navigation (desktop and mobile) - Mobile-first responsive design with dark theme - Show Pro upsell for free tier users to remove platform fee

Co-authored-by: armin.naimi <[email redacted]>