Polish native Settings and live HUD

[yvette-carlisle]

Summary:

• Rework the native Settings surface with flatter, more compact controls and polished glass-aware layout.
• Keep Settings visible and capturable during live capture.
• Tighten live HUD grouping, keycap centering, and position/color spacing.

Validation:

• cargo make fmt-swift
• cargo make build-swift-strict
• cargo make test-host-ffi-header
• cargo test -p rsnap-host-ffi
• cargo make test-macos-native-host-stage
• git diff --check
• ./scripts/build_and_run.sh verify