Polish Screen Recording permission onboarding

[yvette-carlisle]

Summary

• open Screen Recording settings before revealing the floating permission guide
• add the drag-to-grant rsnap floating guide and refine it into a compact horizontal coach mark
• tighten the Settings permissions page and reduce Settings window height without showing a scrollbar

Validation

• cargo make fmt-swift
• cargo make lint-swift-format
• cargo make build-swift-strict
• cargo make lint-swiftlint
• cargo make test-macos-native-host-stage
• git diff --check
• installed and verified /Applications/rsnap.app codesign