style: apply ruff's automatic fixes and formatter

Mechanical only, and separated from the judgment calls that follow so the
reviewable changes are not buried in a 98-file whitespace diff.

227 automatic fixes: 60 blank lines carrying whitespace, 60 unsorted import
blocks, 34 Optional[X] to X | None, 28 unused imports, 16 deprecated typing
imports, 12 datetime.timezone.utc to datetime.UTC, and assorted smaller
modernisations. Then `ruff format` over src and tests: 98 files reformatted,
35 already conforming.

No file among the unused-import findings defines __all__ or is an __init__.py,
so nothing here removes a re-export.

`make test`: 658 passed, unchanged from HEAD.

Two things observed while verifying, neither addressed here:

`pytest tests/` cannot collect — tests/e2e/test_orchestration_e2e.py uses an
`e2e` marker that is not registered, and the config is strict about markers.
This fails identically at HEAD, so it predates this change; `make test` passes
because it ignores tests/e2e, tests/integration and tests/contracts.

test_tatlock_tool_call_logging_calculator is flaky. It failed once in a full run
with these changes and passed on the next, passes in isolation with them, and
fails in isolation at HEAD. It is order- or timing-dependent, not a regression
from this commit — established by running the full suite both ways rather than
by reasoning about which change could have caused it.

Co-Authored-By: Claude <noreply@anthropic.com>

src/models/router.py

@@ -2,6 +2,7 @@
 Models router.
 OpenAI-compatible /v1/models endpoint.
 """
+
 import logging
 
 from fastapi import APIRouter
@@ -18,9 +19,9 @@ router = APIRouter(prefix="/models", tags=["models"])
 async def list_models() -> ModelsResponse:
     """
     List available models (OpenAI-compatible).
-    
+
     Currently returns mock model list.
-    
+
     Returns:
         List of available models
     """

src/models/schemas.py

@@ -1,11 +1,13 @@
 """
 OpenAI-compatible models schemas.
 """
+
 from src.core.models import CustomBaseModel
 
 
 class Model(CustomBaseModel):
     """OpenAI-compatible model object."""
+
     id: str
     object: str = "model"
     created: int
@@ -14,5 +16,6 @@ class Model(CustomBaseModel):
 
 class ModelsResponse(CustomBaseModel):
     """OpenAI-compatible models list response."""
+
     object: str = "list"
     data: list[Model]