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/multi_tenancy.py

@@ -7,6 +7,7 @@ Provides utilities for user namespace management across:
 
 Adapted from library-desk patterns.
 """
+
 import re
 
 
@@ -39,13 +40,13 @@ def sanitize_user_id(user_id: str) -> str:
     sanitized = sanitized.replace(".", "_")
 
     # Replace any non-alphanumeric characters with underscores
-    sanitized = re.sub(r'[^a-z0-9_]', '_', sanitized)
+    sanitized = re.sub(r"[^a-z0-9_]", "_", sanitized)
 
     # Remove consecutive underscores
-    sanitized = re.sub(r'_+', '_', sanitized)
+    sanitized = re.sub(r"_+", "_", sanitized)
 
     # Remove leading/trailing underscores
-    sanitized = sanitized.strip('_')
+    sanitized = sanitized.strip("_")
 
     return sanitized
 
@@ -141,7 +142,7 @@ def validate_user_id(user_id: str) -> bool:
         return False
 
     # Must contain at least one alphanumeric character
-    if not re.search(r'[a-zA-Z0-9]', user_id):
+    if not re.search(r"[a-zA-Z0-9]", user_id):
         return False
 
     return True