- Database section now asks: 'Connection string (DATABASE_URL)' or
  'Individual values (DB_HOST, DB_PORT, DB_NAME, DB_USER, DB_PASSWORD)'
- Connection string mode: asks DATABASE_URL, auto-generates DB_PASSWORD
  for local infra (compose requires POSTGRES_PASSWORD)
- Individual mode: original field-by-field flow
- Fixes 'required variable DB_PASSWORD is missing a value' when starting
  infra after choosing connection string mode