Support hotkey re-registration on keyboard key code changes

[Econa77]

Summary

• add an opt-in autoReRegisterOnKeyboardKeyCodesChange flag to HotKey
• observe NSNotification.Name.SauceSelectedKeyboardKeyCodesChanged and re-register only enabled hot keys whose stored key code no longer matches the current input source
• keep the QWERTY and Dvorak example in the API documentation so the reason for the option is explicit
• enable the option in the example app for the sample hot key

Why

macOS registers the layout-specific key code that is current at registration time. For example, registering v uses KeyCode 9 on a QWERTY layout, but KeyCode 47 on a Dvorak layout. If the selected keyboard key codes change later, the registered hot key can stop pointing at the intended physical key unless it is registered again.

Impact

Existing behavior is unchanged by default. Callers can opt in per hot key when they want automatic re-registration on keyboard key code changes.

Validation

• swift test