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: slower transition + seller settings & academy pages

feat: true iOS-style navigation stack with parallax

fix: MobileNav outside SwipeBack transform + remove duplicate import

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