Revert default_model bump back to gpt-4.1

Coworker review flagged that gpt-5.5 is not a viable default:

- gpt-5 family models require the responses API, but APIProvider has no
  api_type field to signal that — callers using the default would silently
  hit the wrong endpoint shape
- GitHub Models never received gpt-5.5; gpt-4.1 is what's still supported
  there, so 'openai/gpt-5.5' would 404
- Most callers specify models explicitly via model_config anyway, so the
  default is only a fallback safety net — keep it on a model that exists
  on all three providers

Reverts the registry defaults and dataclass default; keeps the gpt-5
prefix in _OpenAIProvider._CHAT_PREFIXES (direct OpenAI API does serve
gpt-5 family, and the prefix check is independent of default selection).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: anticomputer

src/seclab_taskflow_agent/capi.py

@@ -48,7 +48,7 @@ class APIProvider:
     name: str
     base_url: str
     models_catalog: str = "/models"
-    default_model: str = "gpt-5.5"
+    default_model: str = "gpt-4.1"
     extra_headers: Mapping[str, str] = field(default_factory=dict)
     bearer_auth: bool = True  # Use Authorization: Bearer (not x-api-key)
 
@@ -124,20 +124,20 @@ def check_tool_calls(self, _model: str, model_info: dict) -> bool:
     "api.githubcopilot.com": _CopilotProvider(
         name="copilot",
         base_url="https://api.githubcopilot.com",
-        default_model="gpt-5.5",
+        default_model="gpt-4.1",
         extra_headers={"Copilot-Integration-Id": COPILOT_INTEGRATION_ID},
     ),
     "models.github.ai": _GitHubModelsProvider(
         name="github-models",
         base_url="https://models.github.ai/inference",
         models_catalog="/catalog/models",
-        default_model="openai/gpt-5.5",
+        default_model="openai/gpt-4.1",
     ),
     "api.openai.com": _OpenAIProvider(
         name="openai",
         base_url="https://api.openai.com/v1",
         models_catalog="/v1/models",
-        default_model="gpt-5.5",
+        default_model="gpt-4.1",
     ),
 }
 

tests/test_capi_extended.py

@@ -122,7 +122,7 @@ def test_github_models_provider(self):
         p = get_provider("https://models.github.ai/inference")
         assert p.name == "github-models"
         assert p.models_catalog == "/catalog/models"
-        assert p.default_model == "openai/gpt-5.5"
+        assert p.default_model == "openai/gpt-4.1"
 
     def test_openai_provider(self):
         p = get_provider("https://api.openai.com/v1")
@@ -140,7 +140,7 @@ def test_awf_proxy_bare_hostname(self, monkeypatch):
         p = get_provider("http://172.30.0.30:10002")
         assert p.name == "copilot"
         assert p.base_url == "http://172.30.0.30:10002/"
-        assert p.default_model == "gpt-5.5"
+        assert p.default_model == "gpt-4.1"
         assert "Copilot-Integration-Id" in p.extra_headers
 
     def test_awf_proxy_full_url(self, monkeypatch):