fix: allow env var overrides for Nous portal/inference URLs

The _login_nous() call site was pre-filling portal_base_url,
inference_base_url, client_id, and scope with pconfig defaults before
passing them to _nous_device_code_login(). Since pconfig defaults are
always truthy, the env var checks inside the function (HERMES_PORTAL_BASE_URL,
NOUS_PORTAL_BASE_URL, NOUS_INFERENCE_BASE_URL) could never take effect.

Fix: pass None from the call site when no CLI flag is provided, letting
the function's own priority chain handle defaults correctly:
explicit CLI flag > env var > pconfig default.

Addresses the issue reported in PR #5397 by jquesnelle.

hermes_cli/auth.py

@@ -2577,10 +2577,10 @@ def _login_nous(args, pconfig: ProviderConfig) -> None:
 
     try:
         auth_state = _nous_device_code_login(
-            portal_base_url=getattr(args, "portal_url", None) or pconfig.portal_base_url,
-            inference_base_url=getattr(args, "inference_url", None) or pconfig.inference_base_url,
-            client_id=getattr(args, "client_id", None) or pconfig.client_id,
-            scope=getattr(args, "scope", None) or pconfig.scope,
+            portal_base_url=getattr(args, "portal_url", None),
+            inference_base_url=getattr(args, "inference_url", None),
+            client_id=getattr(args, "client_id", None),
+            scope=getattr(args, "scope", None),
             open_browser=not getattr(args, "no_browser", False),
             timeout_seconds=timeout_seconds,
             insecure=insecure,