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

feat: upgraded account page + settings + become-a-seller flow

feat: Google-style top bar + smart FAB visibility

security: fix open redirect + add auth rate limiting

fix: categories page — All tab + empty category + subcategory search

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

feat: slower transition + seller settings & academy pages

fix: iOS nav stack — complete swipe-back + skeleton loader + nav fix

feat: true iOS-style navigation stack with parallax

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

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

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