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)")