SFT-7694 Add registered Miniscript wallet policies

[BitcoinQnA]

Summary

Adds the wallet-layer support used by the Passport Prime Bitcoin app for first-class Miniscript policy accounts.

• Parses and stores registered P2WSH Miniscript policies
• Determines Passport ownership and supports policies containing multiple Passport-derived keys
• Signs compatible policy PSBTs while preserving the registered-policy trust boundary
• Supports signer aliases and policy metadata serialization, including Magic Backup via rkyv
• Adds coverage for common Liana and Nunchuk policy shapes

Scope

This is the lower-level dependency for the KeyOS SFT-7694 implementation. It intentionally does not add a general arbitrary-script signing mode: the policy must be imported and registered before signing.

Verification

• Rebased onto current public main
• cargo test --all-features: 150 passed across all test suites
• cargo clippy --all-targets --all-features -- -D warnings
• Dependent KeyOS Bitcoin app: 50 tests passed, plus ARM and simulator checks
• KeyOS is pinned to commit 0aeac7335dd36104413b477e4f6b03eb8cb30a5a

Linear: https://linear.app/foundation-devices/issue/SFT-7694/featured-miniscript-on-bitcoin-app