Tweak import pubkey from ledger - import after password and only if ledger still available

[monikasmolarek]

Steps:

1. connect the ledger device correctly,
2. click settings->manage keys-> import pub key from the ledger,
3. fill in the name and proceed,
4. on the password validation step disconnect the ledger - physically unplug the device,
5. after that provide a correct password
6. click [import the pub keys from the ledger].

Currently, the pubkey is successfully imported even from a disconnected device.

Expected result:

After physically disconnecting the Ledger device / closing the Spacemesh app / locking the device and providing the correct password, the expected behavior should be: validate the password, handle the disconnection gracefully, and prevent the operation from proceeding with an error indicating the disconnection.
An error message like “Unable to Import Public Keys” should give options to either cancel the operation or retry the connection. The user should not lose any progress made in entering the name and other details, but the import action should be paused until the Ledger is reconnected and the password validated again.