fix(config): accept 'model' key as alias for 'default' in model config (#3603)

Users intuitively write model: { model: my-model } instead of
model: { default: my-model } and it silently falls back to the
hardcoded default. Now both spellings work across all three config
consumers: runtime_provider, CLI, and gateway.

Co-authored-by: ygd58 <ygd58@users.noreply.github.com>

cli.py

@@ -1078,7 +1078,7 @@ class HermesCLI:
         # authoritative.  This avoids conflicts in multi-agent setups where
         # env vars would stomp each other.
         _model_config = CLI_CONFIG.get("model", {})
-        _config_model = _model_config.get("default", "") if isinstance(_model_config, dict) else (_model_config or "")
+        _config_model = (_model_config.get("default") or _model_config.get("model") or "") if isinstance(_model_config, dict) else (_model_config or "")
         _FALLBACK_MODEL = "anthropic/claude-opus-4.6"
         self.model = model or _config_model or _FALLBACK_MODEL
         # Auto-detect model from local server if still on fallback