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/agents/librarian/agent.py

@@ -7,6 +7,7 @@ the library-desk API, offering:
 - Wiki and document management
 - Semantic search and knowledge graph exploration
 """
+
 from typing import Any
 
 from pydantic_ai import Agent
@@ -202,6 +203,7 @@ def _create_librarian_agent() -> Agent[None, str]:
     agent.tool_plain(smart_create_wiki_page)
 
     from src.anthropic.model_selector import get_model_info
+
     model_info = get_model_info()
     logger.info(
         "librarian_agent_created",
@@ -294,6 +296,4 @@ async def run_librarian(
             error=str(e),
             exc_info=True,
         )
-        raise AgentError(
-            "Research task failed", agent_name="librarian"
-        ) from e
+        raise AgentError("Research task failed", agent_name="librarian") from e