usdt deposit refund error is hidden below the fold and cleared by the next refresh #1515

Twin of the iOS issue linked below, found while driving the USDT journeys for synonymdev/bitkit-ios#948. Traced in code on Android master; not reproduced on an Android device.

Observed (iOS) / same code shape on Android

When the service rejects a refund address (UsdtError.InvalidAddress), the user sees no error.

Root cause on Android

• The error renders after the support actions (UsdtDepositsScreen.kt:282, below :276), so it is off-screen.
• DepositPolling (UsdtDepositsScreen.kt:171-187) calls refreshDetail, and updateDetail sets error = null (UsdtDepositViewModel.kt:117), so the message is cleared within ~10 s.

Steps to reproduce

1. Receive USDT on Tron and leave the deposit held.
2. Open Cross-Network Deposits, open the deposit, tap Details.
3. Enter TR7NHqjeKQxGTCi8q8ZY4pL8otSzgjLj6t (the USDT token contract) as the refund address.
4. Tap Request refund and confirm, then scroll to the bottom.

Suggested fix

Show the refund error under the address field, and keep it through background refreshes until the address is edited or the request is retried.

iOS issue: synonymdev/bitkit-ios#960