refactor(schemas): remove NormalizedResponse backward-compat __init__; use canonical API

tests/test_ai_loop_regressions_20260614.py

@@ -19,6 +19,7 @@ from src import ai_client
 from src import thinking_parser
 from src.gui_2 import App
 from src.events import UserRequestEvent
+from src.openai_schemas import UsageStats
 from src.result_types import Result, ErrorInfo, ErrorKind
 
 
@@ -206,10 +207,7 @@ def test_fr3_minimax_thinking_in_returned_text() -> None:
   return Result(data=MagicMock(
    text="The final answer is 42",
    tool_calls=[],
-   usage_input_tokens=0,
-   usage_output_tokens=0,
-   usage_cache_read_tokens=0,
-   usage_cache_creation_tokens=0,
+   usage=UsageStats(input_tokens=0, output_tokens=0, cache_read_tokens=0, cache_creation_tokens=0),
    raw_response=fake_raw,
   ))