DropBridge got safer production routing

We repaired the DropBridge backend history before adding new delivery behavior. Ten production migrations were reconstructed from the remote migration table so local development matched the real Supabase project again.

With history reconciled, we added sender_device_id to uploads. That gives DropBridge a clean way to distinguish the device sending a file from the device meant to receive it, which matters for instant delivery confirmation and for avoiding duplicate or misdirected pickups.

It is backend plumbing, but it protects the thing students actually feel: a PDF leaves Lectra, wakes Scope, downloads on the right computer, and reports back without guesswork.