feat: add Orchestra inbound USDT deposits

[ben-kaufman]

Description

Adds an optional Orchestra client for receiving USDT from Ethereum and TRON into the user's Arbitrum wallet. The client obtains reusable source-network deposit addresses so a sender can make a normal USDT transfer from another wallet.

• Discovers enabled source networks and returns receive instructions with an estimated amount delivered to Arbitrum, applicable amount limits and slippage terms.
• Authenticates deposit registration, history, detail and refund requests using the wallet's derived account.
• Validates the returned network, recipient, amount and deposit terms before exposing receive instructions.
• Provides paginated deposit history, delivery status, transaction references and actionable errors. Explicit refund requests let the user supply a valid address on the deposit's source network.

Based on #158. This PR adds the Rust client and native bindings. The companion backend owns Orchestra credentials, partner integration and refund authorization; native receive screens are maintained separately. The sender remains responsible for the source-network transaction fee.

QA Notes

• Run cargo test --locked --lib modules::usdt, cargo fmt --check and cargo clippy --locked --lib --tests.
• HTTP fixtures cover signed requests, receive-instruction validation, pagination, deposit details, refund requests and provider errors, including amount limits.
• Live deposit delivery and refunds require Flashnet partner approval/provisioning and end-to-end acceptance testing. This PR does not enable partner routes or establish production acceptance.
• Release packaging targets unpublished v0.6.0. Before remote package consumption, build the selected merged source, record the final SwiftPM checksum in a release-preparation commit, and tag/publish that exact iOS archive and matching Android package. Use matching local artifacts for branch testing; later stack layers must use a new version if an earlier layer has already been released.

[ben-kaufman]

Superseded by #164, which implements Rhino inbound USDT deposits independently of the Paykit proof work. Keeping this branch available in case Orchestra support is revisited.