Related issues

• Part of the site-creation onboarding redesign — see the umbrella PR (linked below once open) for the full plan.
• Draft note: based on site-creation-foundation; will be retargeted to trunk and marked ready once wave 1 merges.

How AI was used in this PR

Split out of the workbench/site-creation exploration branch with Claude Code; designed and tested by Shaun on the original branch.

Proposed Changes

• Importing now starts from the drop card on the onboarding home screen, so the import route drops its file-select step and becomes a configure-only page that adopts the dropped backup, seeds a collision-free site name from the filename, and announces progress to screen readers.

Testing Instructions

• From onboarding home, drop (or pick) a backup archive on the "Bring existing" card and complete the import. Try navigating back mid-configure — you should return to home, not an orphaned select step.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?