Dockerfile: backend only — remove Node/npm/frontend build

Hardcode HF Space backend URL — no env var needed

Fix: use Railway PORT env var for next start

Upgrade Next.js to 14.2.35 to fix CVE-2025-55184 and CVE-2025-67779

Connect frontend to HF Space backend via NEXT_PUBLIC_BACKEND_URL env var

Set SPACE_URL env var so embed snippet defaults to HF Space backend URL

Fix: use --extra-index-url for PyTorch so PyPI packages (fastapi etc.) resolve correctly

MVP2: quickAI — AI Copilot for E-Commerce