The async import previously ran fire-and-forget with no way to know
if it succeeded, failed, or was still running.
- Add ImportStatus record (state, message, processed count, startedAt)
and a volatile currentStatus field updated throughout the async run
- POST /api/admin/trigger-import now returns 202 Accepted with initial status
- GET /api/admin/import-status lets callers poll for the current state
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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