fix(cli): support model validation for anthropic_messages and cloudflare-protected endpoints

- probe_api_models: add api_mode param; use x-api-key + anthropic-version
  headers for anthropic_messages mode (Anthropic's native Models API auth)
- probe_api_models: add User-Agent header to avoid Cloudflare 403 blocks
  on third-party OpenAI-compatible endpoints
- validate_requested_model: pass api_mode through from switch_model
- validate_requested_model: for anthropic_messages mode, attempt probe with
  correct auth; if probe fails (many proxies don't implement /v1/models),
  accept the model with an informational warning instead of rejecting
- fetch_api_models: propagate api_mode to probe_api_models

hermes_cli/model_switch.py

@@ -821,6 +821,7 @@ def switch_model(
             target_provider,
             api_key=api_key,
             base_url=base_url,
+            api_mode=api_mode or None,
         )
     except Exception as e:
         validation = {