- Add file type (JPG/PNG/WEBP/PDF) and 5MB size validation
- Show image previews with cleanup of object URLs
- Add data-testid attributes on inputs, buttons, previews, alerts for E2E
- Improve error messaging for expired/failed presigned uploads (403 vs other)
- Guard step 2->3 advance when front image missing
Co-Authored-By: Paperclip <noreply@paperclip.ing>