The 10-photo / 3-video cap was a check-then-insert with no lock on both
upload surfaces, so two overlapping uploads could both take the last slot.
The board media upload and the vendor portal upload now run count, insert
and save inside ExecuteWorkOrderMutationAsync. GetMediaContent maps .heic
to image/heic.
Derive staff vs technician scope from claims (Assigned for User), map
DbUpdateConcurrencyException to a stable 409, and add SQLite competing-write
tests for categorize-vs-categorize and categorize-vs-delete.
