Claude Code harness shows "Could not load live models for this provider"

## Description
When selecting the **Claude Code** ACP harness (`buzz-acp`), the model selector doesn't load live models and instead shows:

> Using built-in model options. Could not load live models for this provider.

## Steps to reproduce
1. Open the harness/agent selector.
2. Choose "Claude Code" as the harness.
3. Observe the model dropdown.

## Expected behavior
Live models for the Claude Code provider load normally, or (if Claude Code manages its own model selection) no error/fallback message is shown.

## Actual behavior
The message "Using built-in model options. Could not load live models for this provider." appears and the harness falls back to a static/built-in model list.

## Environment
- Repo: block/buzz
- Component: buzz-acp (ACP harness — Claude Code)
- Date observed: 2026-07-23

## Additional context
Happy to provide logs or a screenshot if that would help debug.

Reproduce the issue through the harness/agent selector by choosing Claude Code, then trace the buzz-acp model-loading entry point and the fallback message. Determine whether live models should load or Claude Code should suppress the fallback, and verify that the selector no longer shows the misleading error or static fallback when the provider is functioning.

Written by the indexing model from the issue text.