v0.8.0-rc1

Combined prerelease for Bitkit's iOS and Android USDT integration.

• Direct Arbitrum One USDT0 payments with fees paid in USDT.
• Paykit ERC-20 payment-proof signing and verification, including request, billing-period and conversion-quote binding.
• Portable USDT recovery state and backup callbacks for encrypted VSS backup integration.
• Reusable Orchestra deposit addresses and deposit/refund tracking.
• Outbound USDT0 and Orchestra route quotes, with selection based on the recipient amount for the total USDT debit and recovery bound to the selected provider.
• Matching generated Swift and Kotlin interfaces and native packages.

This prerelease combines master (including #165), the unmerged work from #163 (b5267c47) and #167 (c6c987da), and the mobile VSS recovery integration. It is intended for mobile integration and review; publishing it does not merge or approve the pending PRs.

Use 0.8.0-rc1 for both Swift Package Manager and com.synonym:bitkit-core-android. The companion USDT service must support the matching proof receipts and Orchestra APIs.

Validation: 80 USDT tests passed; one existing local-fork test was not run. Rust formatting passed and Clippy introduced no warnings relative to master. The iOS device/simulator XCFramework and four-ABI Android AAR were built and inspected; Android ktlint passed and its six dependency-update notices are in unchanged Gradle files.