feat: SamRock Protocol support for BTCPay Server

[RenAndKiwi]

Summary

• Add SamRock Protocol integration allowing BTCPay Server to generate payment addresses from the user's Bull Bitcoin wallet descriptor
• Accept both BTCPay Server (btc-chain, liquid-chain, btc-ln) and Aqua (btc, lbtc, btcln) URL formats
• Add SamRock entry in Settings screen
• Add paste input alongside QR scanner for URL entry

Test plan

• Tested with live BTCPay Server at btcpay.bitcoinbutlers.com
• Verified invoice payment address matches Bull Bitcoin wallet receive address
• All 16 unit tests pass

[BullishNode]

The samrock protocol normally specifies to create a seperate Liquid Wallet other than the main one (in our case the instant payment wallet). This should be considered as part of our multi-wallet feature.

[RenAndKiwi]

Thanks for the feedback @BullishNode.

We looked into creating a separate Liquid wallet for SamRock. The issue is that lwk.Descriptor.newConfidential() only takes mnemonic + network — it always derives account index 0 (m/84'/1776'/0'). There's no way to create a second Liquid wallet at account index 1 through the current LWK API.

Two options we see:

1. Derive a confidential descriptor at account index 1 outside LWK (manual BIP32 + SLIP77 blinding key derivation), then import it as a watch-only wallet via createPublicWallet. Label it "BTCPay - {serverHost}".

2. Wait for multi-wallet support — if you already have a pattern planned for creating purpose-specific Liquid wallets with custom account indices, we'd rather align with that.

Does LWK support account index selection that we're missing, or do you have a preferred approach in the multi-wallet roadmap?

[BullishNode]

We have a specific approach for multiwallet roadmap we are working on, we will keep you posted. Thanks for the PR! Let's consider that multiwallet feature is a prerequisite for Samrock

[kiwihodl]

@BullishNode should we close this now as this (rockstardev/SamRockProtocol#10) got added and merged?