fix: pass refundOnchainAddress to createOrder

[ovitrif]

Pass a wallet-owned on-chain refund address in CreateOrderOptions.refundOnchainAddress when creating a Blocktank LSP order.

Context

defaultCreateOrderOptions in app/src/main/java/to/bitkit/repositories/BlocktankRepo.kt currently sets refundOnchainAddress to null. Providing the address gives Blocktank a refund destination without requiring the user to contact support and supply one.

Denys confirmed that supplying this field allows Blocktank to automatically create a refund when an order is paid but its channel is not claimed before the order expires.

Acceptance criteria

• Every LSP order creation path supplies a valid address controlled by the user's Bitkit wallet for the active Bitcoin network.
• The address reaches the LSP order endpoint through bitkit-core's CreateOrderOptions.refundOnchainAddress field.
• Address selection follows the wallet's address lifecycle and keeps the supplied address recoverable after restart or wallet restore.
• Address retrieval failures are handled explicitly before order submission.
• Tests verify that order creation sends the wallet's refund address.
• Coordinate with the backend team to verify that a paid, unclaimed order that expires creates a refund to the supplied address and that Bitkit detects the incoming funds.

References

• Support discussion
• LSP request field
• Counterpart: fix: pass refundOnchainAddress to createOrder bitkit-ios#728