feat: Migrate frontend from static HTML to Next.js 16 App Router

feat: Migrate frontend from static HTML to Next.js 16 App Router

feat: Google-style top bar + smart FAB visibility

fix: no transition on reload + AI search fix + skeletons everywhere + hide search btn

feat: slower transition + seller settings & academy pages

feat: premium UX — spotlight search (glassmorphic+stagger), physics loader (draggable C), spring swipe-back, magnetic buttons, optimistic UI bursts, framer-motion page transitions