Add quick screenshot capture mode

[yvette-carlisle]

Summary

• add a quick screenshot acquisition path on Option-Shift-X that preserves menus before drag and enters the normal frozen Rsnap workflow after selection
• keep the frozen follow-up tools by committing a host-owned frozen frame instead of delegating to macOS screencapture
• add configurable quick screenshot shortcut settings and menu binding

Verification

• cargo make fmt-swift
• cargo make check-swift
• cargo make check-vstyle-swift
• cargo make test-macos-native-host
• git diff --check
• ./scripts/build_and_run.sh --verify