fix: resolve 'auto' provider in /model display + update gateway handler

- normalize_provider('auto') now returns 'openrouter' (the default)
  so /model shows the curated model list instead of nothing
- CLI /model display uses normalize_provider before looking up labels
- Gateway /model handler now uses the same validation logic as CLI:
  live API probe, provider:model syntax, curated model list display

hermes_cli/models.py

@@ -126,6 +126,8 @@ def curated_models_for_provider(provider: Optional[str]) -> list[tuple[str, str]
 def normalize_provider(provider: Optional[str]) -> str:
     """Normalize provider aliases to Hermes' canonical provider ids."""
     normalized = (provider or "openrouter").strip().lower()
+    if normalized == "auto":
+        return "openrouter"
     return _PROVIDER_ALIASES.get(normalized, normalized)