fix(auxiliary): skip anthropic in fallback chain when not explicitly configured

_resolve_api_key_provider() now checks is_provider_explicitly_configured
before calling _try_anthropic().  Previously, any auxiliary fallback
(e.g. when kimi-coding key was invalid) would silently discover and use
Claude Code OAuth tokens — consuming the user's Claude Max subscription
without their knowledge.

This is the auxiliary-client counterpart of the setup-wizard gate in
PR #4210.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agent/auxiliary_client.py

@@ -687,6 +687,15 @@ def _resolve_api_key_provider() -> Tuple[Optional[OpenAI], Optional[str]]:
         if pconfig.auth_type != "api_key":
             continue
         if provider_id == "anthropic":
+            # Only try anthropic when the user has explicitly configured it.
+            # Without this gate, Claude Code credentials get silently used
+            # as auxiliary fallback when the user's primary provider fails.
+            try:
+                from hermes_cli.auth import is_provider_explicitly_configured
+                if not is_provider_explicitly_configured("anthropic"):
+                    continue
+            except ImportError:
+                pass
             return _try_anthropic()
 
         pool_present, entry = _select_pool_entry(provider_id)