Preserve keyboard key lifecycle across window focus changes

[botoddly]

Problem

Keyboard input state is tracked per SDL keyboard, while key events are dispatched to the ViewScope of the window identified by each native event. If a key-down handler shows or focuses another application window, focus can change before the corresponding key-up. The release can then target the new window or be absent from the original window input flow, leaving the original press without a matching scoped release and potentially suppressing the next key-down.

This was observed while showing the reusable secondary window added by #405 from a Space key-down handler. That PR avoids the problem by toggling the window on Space key-up, so this is a lower-priority follow-up.

Expected behavior

A logical key press should not remain stuck or lose its release when focus moves between GameKit windows. The view that received key-down should receive either the matching key-up or a focus-loss cancellation represented consistently by the input API.

Possible direction

• record the originating ViewScope for each pressed keyboard/scancode pair
• route a native key-up to the originating scope
• on window focus loss, synthesize releases for keys owned by that scope
• ignore a later unmatched native key-up and prevent repeat events from resurrecting a canceled press
• avoid SDL_ResetKeyboard() because it resets keyboard state globally rather than per window

Coverage

• key-up after an internal window focus change is delivered consistently
• focus loss clears pressed state
• late native key-up does not produce a duplicate release
• repeat after focus loss does not create a new press
• keys owned by another view are unaffected