1. URL imports now participate in upload manager pipeline:
addUrlJob() creates a job row, uploadComplete/setFailed called
on success/failure — consistent with local file uploads
2. activeCount only counts uploading/processing jobs, not failed.
Failed jobs no longer inflate the "Uploads (n)" header count.
3. uploadManager.clear() called on boardId change so stale jobs
from a previous board don't linger in the next board's panel.