Fix: Add NODE_ENV=production during Next.js build to load .env.production

Next.js only loads .env.production when NODE_ENV=production is set during build time.
Previously, NODE_ENV was only set in the runner stage, causing the builder stage to
ignore .env.production and use default values.

This fixes NEXT_PUBLIC_API_URL to correctly point to https://api.lions.dev/btpxpress
instead of just https://api.lions.dev.

Dockerfile

@@ -20,6 +20,7 @@ RUN npm ci
 COPY . .
 
 # Build Next.js application
+ENV NODE_ENV production
 ENV NEXT_TELEMETRY_DISABLED 1
 RUN npm run build