Cleanup / backfill (optional, only if you already have legacy data)

[zigzagdev]

Tasks

• Check if there are existing rows in world_heritage_site_images
• If sort_order is missing/invalid, write a one-time backfill script
  • Reassign order per site (0..N)
• Remove any remaining runtime usage of legacy fields (image_url/primary_image_url) if still referenced