Feature request: Auto-sync theme with system light/dark mode

Feature Request

Description:
Add the ability for Claude Code to automatically switch between light and dark themes based on the operating system's appearance setting.

Current behavior:
Claude Code has a theme setting (light/dark), but it must be changed manually via /config. When running in terminals that don't automatically sync colors (like IntelliJ's integrated terminal), there's no way to have Claude Code follow the system theme.

Problem:
When the system theme changes but Claude Code's theme doesn't update, some text becomes very difficult or impossible to read due to poor contrast (e.g., dark text on a dark background, or light text on a light background). This requires manually running /config to fix, which interrupts the workflow.

Desired behavior:
A new config option like theme: auto or theme: system that would:

• Detect the OS light/dark mode setting
• Automatically switch Claude Code's theme to match
• Ideally respond to system theme changes in real-time (or at minimum, on startup)

Use case:
Users who switch between light and dark mode throughout the day (e.g., based on time of day or ambient lighting) would benefit from Claude Code automatically adapting, especially when using terminals that don't handle this well (like IDE-integrated terminals).

Platform:
macOS (but would also be useful on Windows and Linux)