"Receive"/Import Signed Txn via QR after Txn is Built

**Assumptions**
- User has two separate copies of Specter on two separate laptops (A = Online and B = Offline)
- User signs txns with HWW on the Offline Specter (B)

**Issue: Current Signing Behavior**
- Txn is correctly able to be sent (Exported) from Online Specter A to Offline Specter B via QR (after txn is created)
- After signing the Txn on Offline Specter B, user wants to send Txn back to Online Specter A to broadcast.
- At this step, there is no option to "receive" the signed txn back from Offline Specter B. User has to create a NEW txn on Specter A, and "Import" from B.

**Proposed Solution**
- After Txn is signed by Specter B, have an option to "Receive"/"Import" directly from the details of the created Txn in Specter A.
- Then user can Receive the signed txn without having to create a new one, and then broadcast once received.

Start by tracing the existing QR export flow from the created transaction on the online Specter instance and the corresponding import flow on the offline instance. Determine how the transaction details view represents signing state and where import is currently initiated. Done means a signed transaction can be received directly from the existing transaction details and then broadcast without creating a new transaction.

Written by the indexing model from the issue text.