Image preview works partialy through ghostty + tmux

### Checklist

- [x] I have read through the manual page (`man fzf`)
- [x] I have searched through the existing issues
- [ ] For bug reports, I have checked if the bug is reproducible in the latest version of fzf

### Output of `fzf --version`

0.68.0 (Homebrew)

### OS

- [ ] Linux
- [x] macOS
- [ ] Windows
- [ ] Etc.

### Shell

- [ ] bash
- [x] zsh
- [ ] fish

### Problem / Steps to reproduce

Terminal
Ghostty
❯ ghostty --version
Ghostty 1.2.3

Version
- version: 1.2.3
- channel: stable
Build Config
- Zig version : 0.14.1
- build mode : builtin.OptimizeMode.ReleaseFast
- app runtime : apprt.Runtime.none
- font engine : font.main.Backend.coretext
- renderer : renderer.generic.Renderer(renderer.Metal)
- libxev : kqueue

❯ chafa --version
Chafa version 1.18.1

tmux

run
```
fzf --preview="chafa -f kitty -s \${FZF_PREVIEW_COLUMNS}x\${FZF_PREVIEW_LINES} {}"
```

NOTE
There is whole image outside of tmux.

Start by reproducing the reported fzf --preview command with chafa under Ghostty, macOS, zsh, and tmux, using the listed versions. Compare preview rendering inside and outside tmux; done means the image is contained and rendered correctly in the tmux preview while preserving the reported setup.

Written by the indexing model from the issue text.