TUI text area unreadable with light terminal theme

[callumpbirch]

• HEY CLI version

• macOS + terminal app

• terminal theme: light

• steps:

1. Launch hey
2. Open Journal or compose an email
3. Focus the body field
4. Type text

• actual: body field renders as a black strip and typed text is effectively invisible
• expected: textarea should respect the terminal’s light background / remain readable
• note that it affects both Journal and email composition