fix(doctor): allow vendor slugs for named custom providers

hermes_cli/providers.py

@@ -492,7 +492,10 @@ def get_label(provider_id: str) -> str:
 
 def is_aggregator(provider: str) -> bool:
     """Return True when the provider is a multi-model aggregator."""
-    pdef = get_provider(provider)
+    provider_norm = normalize_provider(provider or "")
+    if provider_norm.startswith("custom:"):
+        return True
+    pdef = get_provider(provider_norm)
     return pdef.is_aggregator if pdef else False