Bulk import existing SDB folders

This scaffolded page marks where the drag-and-drop onboarding flow will live.

Planned workflow

1. Select one PDF, multiple PDFs, or a ZIP archive containing SDB files.
2. Store each file in R2 and enqueue extraction work in the API Worker.
3. Review detected suppliers and confirm source URLs before monitoring begins.

Next implementation tasks

• Swap manual filenames for drag-and-drop PDF selection.
• Replace placeholder target URLs with signed R2 upload URLs.
• Persist upload batches and extraction state in Supabase.