cli: Null stdio handles when spawning Zed on Windows

[Dnreikronos]

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Closes #51101

Release Notes:

• Fixed launching Zed from Git Bash (MinTTY) on Windows leaving a ctrl modifier stuck in the terminal buffer, so the next keystroke after zed was read as Ctrl+key. The CLI now nulls stdio handles when spawning Zed in the background.

Demo

Before:

before.mp4

After:

after.mp4