Ctrl+Space in Windows

[mgreenegit]

On Windows, the current code silently drops or misroutes Ctrl+Space. This PR extracts the per-event decision into a unit-testable
function translate_key_event and normalizes all three forms to NUL (vk::NULL).

This fix was discovered and remediated using Copilot. Human review and feedback requested.

[hiSandog]

For Ctrl+Space on Windows, it would be worth testing the interaction with IME/input-language switching as well as the editor command binding. Some Windows setups reserve that chord for toggling input methods, so the implementation should probably document whether Edit receives the key event only when the terminal passes it through. A small integration note for Windows Terminal vs classic console would make support issues easier to triage.

[mgreenegit]

Added a focused Windows input translation test for the IME/input-language case: if Ctrl+Space/Space arrives with a real produced character, including a non-ASCII IME-style character, Edit preserves it as text input instead of normalizing it to the editor command binding.

Also added a README note documenting the behavior.