CLI looks wrong in xterm with non-UTF charset inside

### Describe the bug

My `$LANG` is set to `uk_UA.KOI8-U` -- and the fonts I'm using with xterm have the matching encoding (koi8-u). Copilot uses wrong symbols for the pseudo-graphics making the screen rather hard to use. Worse, some character-combinations emitted by the program seem to confuse xterm requiring me to reset it.

### Affected version

unknown (cli-0.0.394)

### Steps to reproduce the behavior

The below instructions use Ukrainian as example, but any non-ASCII and non-UTF `LANG`-setting would demonstrate the same behavior.
1. If you don't already have Cyrillic fonts installed -- the `xlsfonts -fn '*fixed*koi8-*'` prints nothing -- install fonts with koi8-u encoding, such as [these](https://www.freshports.org/x11-fonts/geminifonts).
2. Launch xterm using one of such fonts: `xterm -fn '-gemini-fixed-medium-r-normal--20-200-75-75-c-100-koi8-u'`.
3. Set `LANG` environment variable inside the xterm to `uk_UA.KOI8-U`.
4. Start `copilot`.

### Expected behavior

Expecting lines to be drawn as lines, not as sequences of Cyrillic "Б" (see attached snapshot).

### Additional context

使用提供的 koi8-u 字型和 LANG=uk_UA.KOI8-U 在 xterm 中重現問題，然後追蹤 CLI 的終端機呈現與字元編碼路徑。確認修正有效，確保偽圖形呈現為線條，且不需要重設即可繼續使用 xterm。

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