theme: "auto" fails to detect dark background in iTerm2 — no color distinction

[gherkins]

Describe the bug

theme: "auto" produces no color distinction in iTerm2 — all text appears in similar muted tones.
Setting theme: "dark" explicitly in ~/.copilot/config.json restores correct colors immediately.

This is a regression from ~2 versions ago. Same iTerm2 config, same shell (zsh + oh-my-zsh),
colors worked fine before.

Steps to reproduce

1. Use iTerm2 with any dark color scheme
2. Have "theme": "auto" in config (the default)
3. Launch copilot — output has no color distinction

Workaround

Set "theme": "dark" explicitly in ~/.copilot/config.json.

Environment

• Copilot CLI: 1.0.10
• macOS (Darwin), Apple Silicon
• iTerm2 3.6.9
• TERM=xterm-256color (profile), xterm-color (in session)
• COLORTERM=truecolor
• COLORFGBG=15;0 (correctly indicates dark bg)
• Shell: zsh + oh-my-zsh
• Terminal.app with same shell config works fine with auto

[gherkins]

Fix applied:

 - ~/.copilot/config.json: theme: "dark", color_mode: "high-contrast"
 - iTerm2 preset: GitHub Dark (Solarized Dark triggers wrong palette detection in CLI)
 - Must close and reopen iTerm2 tab after changing preset (COLORFGBG is set at tab creation)