User input prompt needs better visual distinction

Problem

In the terminal TUI, user input prompts are visually too similar to AI output. It's hard to quickly scan and find where my messages are in a long conversation.

Current behavior: User input text has minimal visual distinction from Claude's responses — similar dark background, similar text color.

Expected behavior: User input should be clearly distinguishable at a glance (e.g., configurable background color, text color, or border).

Suggested Solution

Add a theme/color configuration option, for example in ~/.claude/settings.json:

{
  "theme": {
    "userInput": {
      "background": "white",
      "foreground": "black"
    }
  }
}

Or even a simple high-contrast toggle that makes user prompts stand out (e.g., inverted colors, bold border, distinct background).

Context

• Terminal: Ghostty (also affects Terminal.app, iTerm2, etc.)
• Since Claude Code controls its own ANSI colors, terminal-level color customization can't fix this.
• The desktop app and VS Code extension handle this well with clear UI separation, but CLI users don't have this option.

Workarounds Tried

• Terminal color profile changes — doesn't help since Claude Code overrides colors
• Custom PS1 — only affects shell prompt, not Claude Code's TUI