Transit shelf registration is effectively an off-shelf operation. Allow
not_shelved, on_shelf, and their mix when target is a transit shelf.
Only transferred items are blocked since they are already in transit.
Also fix conflict color logic: transferred items now correctly show as
red (conflict) for both transit and normal shelf targets.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
In multi-code shelving mode, if the user has scanned zongpai numbers
but hasn't scanned any shelf yet, scanning the first shelf should not
trigger the "switch shelf" warning dialog since there is no existing
shelf to switch from.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
