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/core/exceptions.py

@@ -2,12 +2,13 @@
 Global exception definitions.
 Domain-specific exceptions should be in their respective modules.
 """
+
 from typing import Any
 
 
 class AppException(Exception):
     """Base exception for all application errors."""
-    
+
     def __init__(
         self,
         message: str = "An error occurred",
@@ -22,26 +23,26 @@ class AppException(Exception):
 
 class OllamaConnectionError(AppException):
     """Raised when cannot connect to Ollama service."""
-    
+
     def __init__(self, message: str = "Cannot connect to Ollama service"):
         super().__init__(message=message, status_code=503)
 
 
 class OllamaTimeoutError(AppException):
     """Raised when Ollama request times out."""
-    
+
     def __init__(self, message: str = "Ollama request timed out"):
         super().__init__(message=message, status_code=504)
 
 
 class ModelNotFoundError(AppException):
     """Raised when requested model is not available."""
-    
+
     def __init__(self, model_name: str):
         super().__init__(
             message=f"Model '{model_name}' not found",
             status_code=404,
-            details={"model": model_name}
+            details={"model": model_name},
         )