feat: Add OpenAI API type configuration and update provider settings

tests/config/test_model_presets.py

@@ -1,3 +1,5 @@
+import pytest
+
 from nanobot.config.schema import Config
 
 
@@ -12,6 +14,28 @@ def test_resolve_preset_returns_defaults_when_no_preset() -> None:
     assert resolved.reasoning_effort == config.agents.defaults.reasoning_effort
 
 
+def test_provider_api_type_accepts_exact_values_only() -> None:
+    config = Config.model_validate({
+        "providers": {
+            "openai": {
+                "apiKey": "sk-test",
+                "apiType": "responses",
+            }
+        }
+    })
+    assert config.providers.openai.api_type == "responses"
+
+    with pytest.raises(ValueError):
+        Config.model_validate({
+            "providers": {
+                "openai": {
+                    "apiKey": "sk-test",
+                    "apiType": "response",
+                }
+            }
+        })
+
+
 def test_legacy_defaults_config_without_presets_still_resolves() -> None:
     config = Config.model_validate({
         "agents": {