Implement upload progress UI in image overlay #74363
Description
What problem does this address?
Add visual progress indicators for uploads showing processing and uploading progress.
Acceptance Criteria:
- Minimum requirement is a spinner until all processing is complete
- Ability to cancel in-progress uploads as part of the progress UI
- Accessible status announcements (using wp.speak) - as recommended by accessibility teamj
- Nice to have: Processing stage indication (handing upload X, compressing, generating thumbnail y of z)