chore: prepare production deploy configuration

[emidiovaleretto]

Summary

Adds production configuration for Railway deploy.

Changes

• Updated requirements/production.txt — gunicorn, whitenoise, django-cors-headers
• Updated core/settings/base.py — corsheaders, whitenoise middleware, static files
• Updated core/settings/production.py — CORS, security headers
• Created Procfile — gunicorn + auto-migrate on deploy
• Created railway.json — Railway build config
• Updated .env.example — new variables