fix: /model --global writes model.name instead of model.default

The canonical config key for model name is model.default (used by setup,
auth, runtime_provider, profile list, and CLI startup). But /model --global
wrote to model.name in both gateway and CLI paths.

This caused:
- hermes profile list showing the old model (reads model.default)
- Gateway restart reverting to the old model (_resolve_gateway_model reads model.default)
- CLI startup using the old model (main.py reads model.default)

The only reason it appeared to work in Telegram was the cached agent
staying alive with the in-place switch.

Fix: change all 3 write/read sites to use model.default.

cli.py

@@ -3721,7 +3721,7 @@ class HermesCLI:
 
         # Persistence
         if persist_global:
-            save_config_value("model.name", result.new_model)
+            save_config_value("model.default", result.new_model)
             if result.provider_changed:
                 save_config_value("model.provider", result.target_provider)
             _cprint("    Saved to config.yaml (--global)")

gateway/run.py

@@ -3493,7 +3493,7 @@ class GatewayRunner:
                     cfg = yaml.safe_load(f) or {}
                 model_cfg = cfg.get("model", {})
                 if isinstance(model_cfg, dict):
-                    current_model = model_cfg.get("name", "")
+                    current_model = model_cfg.get("default", "")
                     current_provider = model_cfg.get("provider", current_provider)
                     current_base_url = model_cfg.get("base_url", "")
                 user_provs = cfg.get("providers")
@@ -3603,7 +3603,7 @@ class GatewayRunner:
                 else:
                     cfg = {}
                 model_cfg = cfg.setdefault("model", {})
-                model_cfg["name"] = result.new_model
+                model_cfg["default"] = result.new_model
                 model_cfg["provider"] = result.target_provider
                 if result.base_url:
                     model_cfg["base_url"] = result.base_url