fix: set api_mode when switching providers via hermes model (#3726)

When switching providers via 'hermes model', the previous provider's
api_mode persisted in config.yaml. Switching from Copilot
(codex_responses) to a chat_completions provider like Z.AI would send
requests to the wrong endpoint (404).

Set api_mode = chat_completions in the 4 provider flows that were
missing it: OpenRouter, custom endpoint, Kimi, and api_key_provider.

Co-authored-by: Nour Eddine Hamaidi <HenkDz@users.noreply.github.com>

hermes_cli/main.py

@@ -980,6 +980,7 @@ def _model_flow_openrouter(config, current_model=""):
             cfg["model"] = model
         model["provider"] = "openrouter"
         model["base_url"] = OPENROUTER_BASE_URL
+        model["api_mode"] = "chat_completions"
         save_config(cfg)
         deactivate_provider()
         print(f"Default model set to: {selected} (via OpenRouter)")
@@ -1203,6 +1204,7 @@ def _model_flow_custom(config):
             cfg["model"] = model
         model["provider"] = "custom"
         model["base_url"] = effective_url
+        model["api_mode"] = "chat_completions"
         save_config(cfg)
         deactivate_provider()
 
@@ -1984,6 +1986,7 @@ def _model_flow_kimi(config, current_model=""):
             cfg["model"] = model
         model["provider"] = provider_id
         model["base_url"] = effective_base
+        model["api_mode"] = "chat_completions"
         save_config(cfg)
         deactivate_provider()
 
@@ -2090,6 +2093,7 @@ def _model_flow_api_key_provider(config, provider_id, current_model=""):
             cfg["model"] = model
         model["provider"] = provider_id
         model["base_url"] = effective_base
+        model["api_mode"] = "chat_completions"
         save_config(cfg)
         deactivate_provider()