refactor(ai_client): remove ProviderError class; ErrorInfo is the new error type

tests/test_qwen_provider.py

@@ -39,12 +39,12 @@ def test_qwen_tool_format_translation() -> None:
  assert "parameters" in ds_tools[0]
 
 def test_qwen_error_classification() -> None:
- from src.ai_client import ProviderError
+ from src.result_types import ErrorKind
  from src.qwen_adapter import classify_dashscope_error
  from dashscope.common.error import AuthenticationError
  err = classify_dashscope_error(AuthenticationError("bad key"))
- assert err.kind == "auth"
- assert err.provider == "qwen"
+ assert err.kind == ErrorKind.AUTH
+ assert err.source == "qwen_adapter"
 
 def test_list_qwen_models_returns_hardcoded_registry() -> None:
  from src.ai_client import _list_qwen_models