Add native Unchained Connect Wallet support

[Jacksper13]

Summary

• add Unchained as a native, multisig-only Connect Wallet option
• export the public BIP45 key as a crypto-hdkey QR using the legacy nested tags required by Unchained
• export the existing Sparrow-style BIP45/BIP48 JSON over microSD
• import Unchained wallet registration data through Core's existing multisig QR and microSD parsers
• add regression coverage for the native profile, CBOR payload, raw UR encoding, and Unchained config detection

Compatibility

Unchained sends wallet registration policies as ur:bytes containing its Coldcard-style multisig config. Passport Core already unwraps that payload and accepts the format, so no Unchained-specific parser is introduced. Transaction signing remains on the existing standard PSBT QR and microSD paths.

This is a first-class firmware integration and does not use the extension system.

Testing

• cargo fmt --check
• cargo test --features std
• cbindgen --config cbindgen.toml --crate foundation --output include/foundation.h --verify
• python -m py_compile for the new wallet and unit-test modules
• python -m pycodestyle for the new wallet and unit-test modules
• git diff --check

A full simulator or hardware pairing was not run locally because the Docker simulator and ARM GCC toolchain are unavailable in this environment.