feat: add interactive setup script (./scripts/setup.sh)

Generates .env and nginx.conf by asking:
- Domain name + SSL (Let's Encrypt)
- Database (bundled PostgreSQL or external)
- Security (auto-generates JWT secret + DB password)
- Compute resources (threads, max jobs, gpredomics version)
- Optional: SMTP email, scitq distributed computing
- Backup retention

Usage: ./scripts/setup.sh

Author: eprifti