/agents shows empty list when only plugin agents exist, appears as broken arrow keys

Problem

When a project has agents provided only by plugins (not local .claude/agents/ files), running /agents shows an empty interactive list. Since there are no items to navigate, arrow keys appear to do nothing — making it look like a keybinding/input bug rather than an empty state.

This is confusing because the agents do exist and are usable, they just aren't editable.

Expected behavior

When no editable (local) agents exist, /agents should display a clear message like:

"No editable agents found. Plugin agents cannot be edited from here."

This would prevent confusion and make it obvious that the empty list is intentional, not a broken UI.

Steps to reproduce

1. Install a plugin that provides agents (e.g., one with .claude-plugin/agents/ definitions)
2. Ensure the project has no local agents in .claude/agents/
3. Run /agents
4. Observe an empty interactive list where arrow keys appear non-functional