Fix native text input SendInput layout

[enaboapps]

Summary

The isolated native text input proof found that the Windows INPUT union in the text helper is too small on x64. SendInput returns error 87 until the union reserves the full native size.

Scope

• Set the native text helper input union size correctly for x64.
• Keep the native Unicode text input protocol unchanged.
• Validate with the isolated proof harness and repo checks.

Acceptance criteria

• SwitchifyTextInput.exe can send Unicode text through SendInput without clipboard fallback.
• Native helper smoke check passes.
• npm test passes.
• npm run build passes.
• npm run native:build passes.