Switch Voxit to native macOS host

[yvette-carlisle]

Summary

• replace the legacy Rust app shell with a SwiftPM macOS menu bar host backed by a Rust C ABI snapshot bridge
• add repo-managed Dock and menu bar icon assets, including source and generated outputs
• update docs, release packaging, and repo-native gates for the native host path

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make checks
• ./scripts/build_and_run.sh run
• codesign verification for target/voxit-native-host/Voxit.app