[UI Bug] No visual selection indicator in /agents library navigation

Description

When opening the /agents dialog and navigating the agent library with arrow keys, there is no visible highlight or focus indicator showing which item is currently selected. Navigation works functionally (pressing Enter selects the agent), but the user has no visual feedback about which item is focused until after entering the agent's submenu.

Steps to Reproduce

1. Open Claude Code
2. Type /agents or use the agents command
3. Navigate to the agent library
4. Use arrow keys (↑/↓) to scroll through the list

Expected Behavior

The currently focused/selected agent should be visually highlighted (e.g., background color, border, or cursor indicator).

Actual Behavior

No visual indicator is shown. The user can press Enter and the agent gets selected, but there is no way to know which item is focused while navigating the list.

Environment

• OS: Windows 11 Pro (10.0.26200)
• Claude Code version: 2.1.126
• Terminal: PowerShell

Additional Context

The issue appears only in the agent library list. Basic navigation functionality (arrow keys, Enter) works correctly.