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

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

security: fix open redirect + add auth rate limiting

feat: true iOS-style navigation stack with parallax

security: remove hardcoded NVIDIA API key — use env var

feat: fast AI via Llama-3.1-8B direct (1-3s), vision relay via Llama-3.2-11B, product search in parallel

fix: map edge function response field names (response → reply)

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

fix: Flatten nested src/src/ and public/public/, remove invalid eslint config key