Allow disabling or restyling the agent-name badge in transcript

Summary

When agents are spawned (via the Agent tool, /loop, etc.), their names are rendered in the transcript with a solid colored background — e.g. paper-section-revisor on a blue block, irf-runner on a green block. With multiple agents running in parallel, the transcript ends up with several large colored rectangles that visually dominate the surrounding text.

I'd like a way to either disable the background highlight entirely or restyle it (e.g. foreground color only, or a subtle dim style).

Proposed options

Any of these would work, in rough order of preference:

1. A settings.json toggle, e.g. "ui.agentBadgeStyle": "background" | "foreground" | "none".
2. Respect terminal theme — use the theme's accent color as foreground instead of a hardcoded background.
3. A NO_COLOR-style env var scoped to agent badges only.

Environment

• Claude Code 2.1.143 (compiled binary, macOS arm64)
• Terminal: Ghostty
• Dark theme

Why not patch it locally

v2.x ships as a single Bun-compiled Mach-O binary, so users can't patch the rendering logic the way they could with the older Node-based cli.js. A built-in setting is the only realistic path.